/* 
  HỌC TOÁN CÙNG THẦY AN — HỆ THỐNG GIAO DIỆN CHUẨN EDTECH CAO CẤP
  Thiết kế sang trọng, hiện đại, tối ưu cho học tập tập trung & bảo mật bản quyền
*/

@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;600;700;800&family=Plus+Jakarta+Sans:ital,wght@0,400;0,500;0,600;0,700;0,800;1,400;1,600&display=swap');

:root {
  /* ================= DESIGN SYSTEM TOKENS (LIGHT THEME) ================= */
  --bg-page: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-elevated: #ffffff;
  --bg-surface-soft: #f1f5f9;
  --bg-sidebar: #ffffff;
  --text-main: #0f172a;
  --text-secondary: #334155;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  --border-subtle: #f1f5f9;

  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --primary-dark: #1e3a8a;
  --primary-gradient: linear-gradient(135deg, #1e3a8a 0%, #2563eb 50%, #38bdf8 100%);
  --accent-cyan: #0284c7;
  --accent-cyan-light: #f0f9ff;
  --secondary: #10b981;
  --secondary-light: #ecfdf5;
  --accent: #f59e0b;
  --accent-amber: #f59e0b;
  --accent-amber-light: #fffbeb;
  --accent-orange: #ea580c;
  --accent-red: #ef4444;
  --dark: #090d16;
  --slate: #1e293b;
  --slate-600: #475569;
  --muted: #64748b;
  --light: #f8fafc;
  --border: #e2e8f0;
  --border-light: rgba(226, 232, 240, 0.8);
  --white: #ffffff;
  --cinema-bg: #0b0f19;
  --cinema-surface: #111827;
  --cinema-border: #1f2937;
  --shadow-xs: 0 1px 2px 0 rgba(15, 23, 42, 0.05);
  --shadow-sm: 0 2px 4px -1px rgba(15, 23, 42, 0.06), 0 1px 2px -1px rgba(15, 23, 42, 0.04);
  --shadow: 0 4px 12px -2px rgba(15, 23, 42, 0.08), 0 2px 6px -1px rgba(15, 23, 42, 0.04);
  --shadow-md: 0 8px 20px -4px rgba(15, 23, 42, 0.08), 0 4px 10px -2px rgba(15, 23, 42, 0.04);
  --shadow-lg: 0 16px 32px -6px rgba(15, 23, 42, 0.12), 0 6px 16px -4px rgba(15, 23, 42, 0.06);
  --shadow-glow-blue: 0 0 24px -4px rgba(37, 99, 235, 0.35);
  --shadow-glow-cyan: 0 0 24px -4px rgba(6, 182, 212, 0.35);
  --shadow-glow-amber: 0 0 24px -4px rgba(245, 158, 11, 0.35);
  --radius-lg: 16px;
  --radius: 12px;
  --radius-sm: 8px;
  --radius-full: 9999px;
  --star-color: #f59e0b;
  --bg-frosted: rgba(255, 255, 255, 0.94);
  --accent-red-light: #fef2f2;
  --accent-orange-light: #fff7ed;
  --text-on-primary: #ffffff;
  --text-on-dark-surface: #f8fafc;
  --scrollbar-track: #f1f5f9;
  --scrollbar-thumb: #cbd5e1;
  --scrollbar-thumb-hover: #94a3b8;
  --trap-bg: rgba(225, 29, 72, 0.07);
  --trap-color: #be123c;
  --trap-border: rgba(225, 29, 72, 0.22);
}

/* ================= DARK MODE TOKENS (CHẾ ĐỘ TỐI) ================= */
[data-theme="dark"] {
  --bg-page: #0b0f19;
  --bg-surface: #111827;
  --bg-surface-elevated: #1a233a;
  --bg-surface-soft: #1e293b;
  --bg-sidebar: #111827;
  --text-main: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --border-color: #1e293b;
  --border-subtle: #1e293b;

  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-light: rgba(59, 130, 246, 0.15);
  --primary-dark: #1d4ed8;

  --secondary: #34d399;
  --secondary-light: rgba(52, 211, 153, 0.15);

  --dark: #f8fafc;
  --slate: #cbd5e1;
  --slate-600: #94a3b8;
  --muted: #94a3b8;
  --light: #0b0f19;
  --border: #1e293b;
  --border-light: rgba(30, 41, 59, 0.8);
  --white: #111827;

  --shadow-sm: 0 2px 6px rgba(0, 0, 0, 0.4);
  --shadow: 0 4px 16px rgba(0, 0, 0, 0.45);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 16px 36px rgba(0, 0, 0, 0.6);

  --bg-frosted: rgba(17, 24, 39, 0.94);
  --accent-red-light: rgba(239, 68, 68, 0.12);
  --accent-orange-light: rgba(234, 88, 12, 0.12);
  --accent-amber-light: rgba(245, 158, 11, 0.12);
  --accent-cyan-light: rgba(6, 182, 212, 0.12);
  --trap-bg: rgba(244, 63, 94, 0.12);
  --trap-color: #fda4af;
  --trap-border: rgba(244, 63, 94, 0.3);
  --text-on-primary: #ffffff;
  --text-on-dark-surface: #f8fafc;
  --scrollbar-track: #1e293b;
  --scrollbar-thumb: #334155;
  --scrollbar-thumb-hover: #475569;
  --cinema-bg: #0b0f19;
  --cinema-surface: #111827;
  --cinema-border: #1f2937;
}

/* Cinema Light Mode: phòng học sáng khi user chọn light theme */
[data-theme="light"] {
  --cinema-bg: #f1f5f9;
  --cinema-surface: #ffffff;
  --cinema-border: #e2e8f0;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* ================= ADOBE REACT-ARIA & MOBILE-FIRST TOUCH CORE ================= */
button, a, input, select, textarea, [role="button"], .btn {
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
}

@media (pointer: coarse) {
  /* Phản hồi chạm chân thực trên thiết bị cảm ứng di động */
  button:active, .btn:active, [role="button"]:active {
    transform: scale(0.97);
    transition: transform 0.1s ease-out;
  }
}

@media (max-width: 768px) {
  /* Chống iOS Safari tự động zoom làm vỡ giao diện */
  input, select, textarea {
    font-size: 16px !important;
  }
}

html {
  overflow-x: clip;
  width: 100%;
  max-width: 100vw;
  scroll-behavior: smooth;
  min-height: 100%;
}

body {
  font-family: 'Plus Jakarta Sans', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background-color: var(--bg-page);
  color: var(--text-secondary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: clip;
  width: 100%;
  max-width: 100vw;
  min-height: 100vh;
  min-height: 100dvh;
  transition: background-color 0.25s ease, color 0.25s ease;
}

a {
  text-decoration: none;
  color: inherit;
}

.container {
  width: 100%;
  max-width: 1440px;
  margin: 0 auto;
  padding: 0 clamp(16px, 2.5vw, 40px);
}

/* ================= ANNOUNCEMENT BAR ================= */
.announcement-bar {
  background: linear-gradient(90deg, #1e3a8a 0%, #2563eb 45%, #7c3aed 100%);
  color: #ffffff;
  padding: max(9px, env(safe-area-inset-top, 0px)) max(16px, env(safe-area-inset-right, 0px)) 9px max(16px, env(safe-area-inset-left, 0px));
  font-size: 0.88rem;
  font-weight: 600;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  letter-spacing: 0.2px;
  flex-wrap: wrap;
  z-index: 1001;
  position: relative;
  box-shadow: 0 2px 8px rgba(30, 58, 138, 0.25);
}

.announcement-badge {
  background: rgba(254, 240, 138, 0.22);
  border: 1px solid rgba(254, 240, 138, 0.4);
  color: #fef08a;
  padding: 3px 10px;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.countdown-pill {
  background: rgba(15, 23, 42, 0.45);
  backdrop-filter: blur(8px);
  padding: 4px 14px;
  border-radius: var(--radius-full);
  font-size: 0.82rem;
  font-weight: 700;
  display: inline-flex;
  align-items: center;
  gap: 5px;
  border: 1px solid rgba(255, 255, 255, 0.22);
  box-shadow: inset 0 1px 2px rgba(0,0,0,0.3);
}

.countdown-label {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.6px;
  opacity: 0.9;
  margin-right: 4px;
}

.countdown-val {
  background: var(--bg-surface);
  color: #1e3a8a;
  padding: 2px 6px;
  border-radius: 5px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.86rem;
  font-weight: 800;
  min-width: 24px;
  text-align: center;
  display: inline-block;
  line-height: 1.25;
  box-shadow: 0 1px 3px rgba(0,0,0,0.2);
}

.countdown-unit {
  font-size: 0.72rem;
  opacity: 0.85;
  margin-right: 2px;
}

/* ================= HEADER / NAVBAR ================= */
.header {
  background: var(--bg-surface);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 1000;
  padding-left: env(safe-area-inset-left, 0px);
  padding-right: env(safe-area-inset-right, 0px);
  transition: background-color 0.25s ease, border-color 0.25s ease;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: clamp(18px, 2.2vw, 36px);
  height: 72px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 1.25rem;
  font-weight: 800;
  background: var(--primary-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  letter-spacing: -0.5px;
  white-space: nowrap;
  flex-shrink: 0;
}

.logo-icon {
  font-size: 1.8rem;
  -webkit-text-fill-color: initial;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-link {
  font-weight: 600;
  font-size: 0.92rem;
  color: var(--slate);
  transition: all 0.2s;
  padding: 6px 10px;
  border-radius: 6px;
  white-space: nowrap;
  flex-shrink: 0;
}

.nav-link:hover, .nav-link.active {
  color: var(--primary);
  background: var(--primary-light);
}

.auth-box {
  display: flex;
  align-items: center;
  gap: 10px;
  white-space: nowrap;
  flex-shrink: 0;
}

.lang-switcher-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  background: var(--white);
  border: 1.5px solid var(--border);
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--slate);
  transition: all 0.2s;
  white-space: nowrap;
  flex-shrink: 0;
}

.lang-switcher-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
  transform: translateY(-1px);
}

.theme-toggle-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: var(--white);
  border: 1.5px solid var(--border);
  border-radius: 50%;
  cursor: pointer;
  font-size: 1.05rem;
  color: var(--slate);
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  white-space: nowrap;
  flex-shrink: 0;
}

.theme-toggle-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
  transform: translateY(-1px) scale(1.05);
  box-shadow: 0 3px 10px rgba(37, 99, 235, 0.2);
}

.header-qr-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  background: var(--white);
  border: 1.5px solid var(--border);
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--slate);
  transition: all 0.2s;
  white-space: nowrap;
  flex-shrink: 0;
  height: 38px;
}

.header-qr-pill:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
  transform: translateY(-1px);
  box-shadow: 0 2px 8px rgba(37, 99, 235, 0.12);
}

@media (max-width: 1260px) {
  .header-qr-pill .qr-pill-label {
    display: none;
  }
  .header-qr-pill {
    padding: 6px 10px;
  }
}

/* ============ HYBRID MULTI-LANGUAGE DROPDOWN POPOVER ============ */
/* ============ HYBRID MULTI-LANGUAGE DROPDOWN POPOVER ============ */
.lang-menu-popover {
  display: none;
  position: fixed;
  background: var(--bg-surface);
  border-radius: 14px;
  box-shadow: 0 14px 35px -5px rgba(0, 0, 0, 0.22), 0 8px 16px -6px rgba(0, 0, 0, 0.12);
  border: 1px solid var(--border-color);
  padding: 12px;
  z-index: 10000;
  font-family: inherit;
  animation: langFadeIn 0.18s ease-out forwards;
  width: 350px;
  max-width: 92vw;
  box-sizing: border-box;
}

.lang-menu-popover.active {
  display: block;
}

@keyframes langFadeIn {
  from { opacity: 0; transform: translateY(-6px); }
  to { opacity: 1; transform: translateY(0); }
}

.lang-menu-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: 8px;
  border-bottom: 1px solid #f1f5f9;
  font-size: 0.74rem;
  font-weight: 800;
  color: var(--slate-600);
  letter-spacing: 0.5px;
}

.lang-menu-close {
  background: none;
  border: none;
  font-size: 0.95rem;
  color: var(--text-muted);
  cursor: pointer;
  padding: 2px 6px;
  border-radius: 4px;
  transition: all 0.15s;
}

.lang-menu-close:hover {
  background: var(--bg-surface-soft);
  color: var(--text-secondary);
}

/* Ô tìm kiếm ngôn ngữ */
.lang-search-wrapper {
  position: relative;
  display: flex;
  align-items: center;
  margin: 10px 0 8px 0;
}

.lang-search-icon {
  position: absolute;
  left: 10px;
  font-size: 0.85rem;
  color: var(--text-muted);
  pointer-events: none;
}

.lang-search-input {
  width: 100%;
  padding: 8px 30px 8px 32px;
  font-family: inherit;
  font-size: 14px;
  color: var(--slate);
  background: var(--bg-page);
  border: 1px solid #cbd5e1;
  border-radius: 8px;
  outline: none;
  transition: all 0.2s ease;
  box-sizing: border-box;
}

@media (max-width: 768px) {
  .lang-search-input {
    font-size: 16px !important;
    min-height: 44px;
  }
}

.lang-search-input:focus {
  background: var(--bg-surface);
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.15);
}

.lang-search-clear {
  position: absolute;
  right: 6px;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 0.8rem;
  cursor: pointer;
  padding: 3px 6px;
  border-radius: 50%;
  line-height: 1;
}

.lang-search-clear:hover {
  color: var(--text-secondary);
  background: var(--bg-surface-soft);
}

.lang-search-result-count {
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--primary);
  margin: 4px 0 6px 4px;
}

.lang-search-empty {
  text-align: center;
  padding: 24px 12px;
  color: var(--text-muted);
  font-size: 0.82rem;
}

.lang-menu-section-title {
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--text-muted);
  margin: 8px 0 6px 4px;
  letter-spacing: 0.3px;
}

.lang-menu-core-group {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.lang-menu-item.core-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 10px;
  background: var(--bg-page);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  cursor: pointer;
  text-align: left;
  transition: all 0.15s;
  width: 100%;
  box-sizing: border-box;
}

.lang-menu-item.core-item:hover {
  background: var(--primary-light);
  border-color: var(--primary);
  transform: translateX(2px);
}

.lang-menu-item.core-item.active {
  background: var(--primary-light);
  border-color: var(--primary);
  box-shadow: 0 0 0 1px #3b82f6;
}

.lang-menu-item .flag {
  font-size: 1.25rem;
  line-height: 1;
}

.lang-menu-item .info {
  flex: 1;
  min-width: 0;
}

.lang-menu-item .name {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--slate);
  display: flex;
  align-items: center;
  gap: 6px;
}

.lang-menu-item .badge-core {
  font-size: 0.62rem;
  background: var(--primary-light);
  color: var(--primary-dark);
  padding: 1px 5px;
  border-radius: 4px;
  font-weight: 600;
}

.lang-menu-item .desc {
  font-size: 0.68rem;
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.lang-menu-item .check {
  font-weight: 800;
  color: var(--primary);
  font-size: 1rem;
}

.lang-menu-scrollable-container {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 6px;
  max-height: 230px;
  overflow-y: auto;
  padding-right: 3px;
}

/* Custom Scrollbar */
.lang-menu-scrollable-container::-webkit-scrollbar {
  width: 5px;
}

.lang-menu-scrollable-container::-webkit-scrollbar-track {
  background: var(--bg-surface-soft);
  border-radius: 4px;
}

.lang-menu-scrollable-container::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

.lang-menu-scrollable-container::-webkit-scrollbar-thumb:hover {
  background: #94a3b8;
}

.lang-other-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 8px;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  font-size: 0.76rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.15s;
  text-align: left;
  box-sizing: border-box;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.lang-other-btn:hover {
  background: var(--bg-page);
  border-color: var(--border);
}

.lang-other-btn.active {
  background: var(--primary-light);
  border-color: var(--primary);
  color: var(--primary-dark);
  box-shadow: 0 0 0 1px #3b82f6;
}

.lang-other-btn .flag {
  font-size: 1rem;
  line-height: 1;
  flex-shrink: 0;
}

.lang-other-btn .text {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.lang-menu-footer {
  margin-top: 10px;
  padding-top: 8px;
  border-top: 1px solid #f1f5f9;
  font-size: 0.68rem;
  color: var(--text-muted);
  text-align: center;
  line-height: 1.35;
}

/* Ẩn banner mặc định gây xô lệch giao diện của Google Translate */
.goog-te-banner-frame.skiptranslate,
.goog-te-banner-frame {
  display: none !important;
}

body {
  top: 0px !important;
}

.goog-tooltip,
.goog-tooltip:hover {
  display: none !important;
}

.goog-text-highlight {
  background-color: transparent !important;
  border: none !important;
  box-shadow: none !important;
}

#google_translate_element_hidden {
  display: none;
}


.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 22px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  border: none;
  transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

.btn-primary {
  background: var(--primary-gradient);
  color: var(--white);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.25);
}

@media (hover: hover) and (pointer: fine) {
  .btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(37, 99, 235, 0.35);
  }
  .btn-outline:hover {
    border-color: var(--primary);
    color: var(--primary);
    background: var(--primary-light);
  }
  .btn-success:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(5, 150, 105, 0.35);
  }
}

@media (pointer: coarse) {
  .btn:active, .btn-primary:active, .btn-outline:active, .btn-success:active {
    transform: scale(0.97);
  }
}

.user-profile {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--white);
  padding: 4px 12px 4px 6px;
  border: 1px solid var(--border);
  border-radius: 30px;
}

.user-avatar {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 2px solid #38bdf8;
  object-fit: cover;
}

/* ================= HERO SECTION (VISUAL WOW UPGRADE) ================= */
.hero {
  padding: 60px 0 75px;
  background: 
    radial-gradient(ellipse 80% 50% at 50% -15%, rgba(37, 99, 235, 0.16), transparent 70%),
    radial-gradient(circle at 92% 35%, rgba(6, 182, 212, 0.12), transparent 45%),
    radial-gradient(circle at 8% 75%, rgba(16, 185, 129, 0.08), transparent 45%),
    #f8fafc;
  position: relative;
  overflow: hidden;
  border-bottom: 1px solid rgba(226, 232, 240, 0.9);
}

/* Ambient Math Grid Backdrop Pattern */
.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image: 
    linear-gradient(to right, rgba(148, 163, 184, 0.09) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(148, 163, 184, 0.09) 1px, transparent 1px);
  background-size: 36px 36px;
  pointer-events: none;
  mask-image: radial-gradient(ellipse 80% 70% at 50% 40%, #000 50%, transparent 100%);
  -webkit-mask-image: radial-gradient(ellipse 80% 70% at 50% 40%, #000 50%, transparent 100%);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 40px;
  align-items: center;
  position: relative;
  z-index: 2;
}

/* HERO TOÀN DIỆN CHO NGƯỜI MẤT GỐC (FULL-WIDTH CENTERED) */
.hero-full-width {
  padding: 32px 0 56px;
}

.hero-content-full {
  max-width: 920px;
  margin: 0 auto;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  position: relative;
  z-index: 2;
}

.hero-content-full .hero-title {
  font-size: clamp(2.1rem, 3.2vw, 3rem);
  line-height: 1.25;
  margin-bottom: 14px;
  text-wrap: balance;
}

.hero-content-full .hero-subtitle {
  max-width: 800px;
  font-size: 1.1rem;
  line-height: 1.65;
  color: var(--slate-600);
  margin-bottom: 18px;
}

.hero-guarantee-pills {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 10px;
  margin-bottom: 22px;
}

.guarantee-pill-item {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 18px;
  background: var(--bg-frosted);
  border: 1.5px solid #cbd5e1;
  border-radius: 9999px;
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--slate);
  box-shadow: 0 4px 14px rgba(15, 23, 42, 0.04);
  backdrop-filter: blur(8px);
  transition: all 0.25s ease;
}

.guarantee-pill-item:hover {
  border-color: var(--primary);
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(37, 99, 235, 0.12);
}

.hero-actions-center {
  justify-content: center;
  width: 100%;
}

.hero-trust-center {
  justify-content: center;
  margin-top: 16px;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 16px;
  background: rgba(37, 99, 235, 0.08);
  border: 1px solid rgba(37, 99, 235, 0.28);
  color: var(--primary-dark);
  font-weight: 700;
  font-size: 0.88rem;
  border-radius: 9999px;
  margin-bottom: 14px;
  box-shadow: 0 2px 10px rgba(37, 99, 235, 0.1);
  backdrop-filter: blur(8px);
  animation: badgeFloat 3.5s ease-in-out infinite alternate;
}

@keyframes badgeFloat {
  0% { transform: translateY(0px); }
  100% { transform: translateY(-4px); }
}

.hero-title {
  font-size: clamp(2.2rem, 3vw, 2.9rem);
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.22;
  margin-bottom: 18px;
  letter-spacing: -0.8px;
  text-wrap: balance;
}

.hero-title-line {
  display: block;
}

.text-holographic {
  background: linear-gradient(135deg, #0f172a 0%, #1d4ed8 45%, #06b6d4 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  display: inline-block;
}

.hero-title span.brand-glow {
  background: linear-gradient(135deg, #2563eb 0%, #06b6d4 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  text-shadow: 0 0 20px rgba(6, 182, 212, 0.3);
}

.hero-subtitle {
  font-size: 1.15rem;
  color: var(--slate-600);
  margin-bottom: 28px;
  line-height: 1.7;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  margin-bottom: 24px;
}

.btn-buy-lg {
  background: linear-gradient(135deg, #f97316 0%, #ea580c 50%, #dc2626 100%);
  color: var(--text-on-primary);
  padding: 15px 32px;
  font-size: 1.05rem;
  font-weight: 700;
  border-radius: var(--radius);
  box-shadow: 0 8px 22px -4px rgba(234, 88, 12, 0.45), 0 2px 6px rgba(0,0,0,0.06);
  transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

.btn-buy-lg:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 30px -4px rgba(234, 88, 12, 0.55), 0 4px 10px rgba(0,0,0,0.1);
}

.btn-outline-trial {
  background: var(--bg-frosted);
  backdrop-filter: blur(8px);
  border: 1.5px solid #cbd5e1;
  color: var(--slate);
  padding: 15px 28px;
  font-size: 1.05rem;
  font-weight: 700;
  border-radius: var(--radius);
  box-shadow: 0 4px 12px rgba(15, 23, 42, 0.05);
  transition: all 0.25s;
}

.btn-outline-trial:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
  transform: translateY(-2px);
}

/* Trust Avatars */
.hero-trust {
  display: flex;
  align-items: center;
  gap: 14px;
  padding-top: 16px;
  border-top: 1px solid rgba(226, 232, 240, 0.8);
}

.avatar-stack {
  display: flex;
  align-items: center;
}

.avatar-stack img {
  width: 38px;
  height: 38px;
  border-radius: 50%;
  border: 2px solid var(--bg-surface);
  margin-left: -10px;
  object-fit: cover;
  box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.avatar-stack img:first-child {
  margin-left: 0;
}

.trust-text {
  font-size: 0.88rem;
  color: var(--slate);
  font-weight: 600;
}

.trust-text span {
  color: var(--primary);
  font-weight: 800;
}

/* ================= INTERACTIVE 3D MATH SANDBOX CARD ================= */
.math-sandbox-card {
  background: var(--bg-frosted);
  backdrop-filter: blur(16px);
  border: 1px solid rgba(226, 232, 240, 0.9);
  border-radius: 20px;
  padding: 20px;
  box-shadow: 
    0 25px 50px -12px rgba(15, 23, 42, 0.15),
    0 0 0 1px rgba(255, 255, 255, 0.8) inset;
  position: relative;
  transition: all 0.3s ease;
}

.math-sandbox-card:hover {
  box-shadow: 
    0 30px 60px -12px rgba(37, 99, 235, 0.2),
    0 0 0 1px rgba(56, 189, 248, 0.3) inset;
}

.sandbox-tabs {
  display: flex;
  gap: 6px;
  background: var(--bg-surface-soft);
  padding: 4px;
  border-radius: 12px;
  margin-bottom: 12px;
}

.sandbox-tab-btn {
  flex: 1;
  padding: 7px 8px;
  font-size: 0.8rem;
  font-weight: 700;
  border: none;
  background: transparent;
  color: var(--text-muted);
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
  text-align: center;
  white-space: nowrap;
}

.sandbox-tab-btn:hover {
  color: var(--slate);
}

.sandbox-tab-btn.active {
  background: var(--bg-surface);
  color: var(--primary-dark);
  box-shadow: 0 2px 6px rgba(0,0,0,0.08);
}

.preview-badge-live {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--accent-red-light);
  color: #dc2626;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 20px;
}

.preview-badge-live::before {
  content: "";
  width: 8px;
  height: 8px;
  background: #dc2626;
  border-radius: 50%;
  animation: pulse 1.5s infinite;
}

@keyframes pulse {
  0% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(220, 38, 38, 0.7); }
  70% { transform: scale(1); box-shadow: 0 0 0 8px rgba(220, 38, 38, 0); }
  100% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(220, 38, 38, 0); }
}

.preview-mockup-frame {
  width: 100%;
  height: 220px;
  background: radial-gradient(circle at center, #111827 0%, #030712 100%);
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 14px;
  position: relative;
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-on-primary);
  margin-bottom: 14px;
  box-shadow: inset 0 2px 10px rgba(0,0,0,0.5);
}

.preview-play-btn {
  width: 56px;
  height: 56px;
  background: var(--bg-frosted);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--primary);
  font-size: 1.5rem;
  box-shadow: 0 0 25px rgba(56, 189, 248, 0.6);
  transition: all 0.3s ease;
  cursor: pointer;
}

.preview-mockup-frame:hover .preview-play-btn {
  transform: scale(1.1);
  box-shadow: 0 0 35px rgba(56, 189, 248, 0.85);
}

/* ================= STATS BAR (FROSTED GLASS 3D - 3 CỘT CÂN ĐỐI) ================= */
.stats-bar {
  background: var(--bg-frosted);
  backdrop-filter: blur(16px);
  border: 1px solid rgba(226, 232, 240, 0.9);
  border-radius: 24px;
  padding: 26px 36px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-top: -38px;
  position: relative;
  z-index: 20;
  box-shadow: 
    0 20px 40px -15px rgba(15, 23, 42, 0.12),
    0 0 0 1px rgba(255, 255, 255, 0.8) inset;
}

.stat-item {
  display: flex;
  align-items: center;
  gap: 16px;
}

.stat-icon {
  font-size: 2.2rem;
  background: linear-gradient(135deg, #eff6ff 0%, #e0f2fe 100%);
  width: 56px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 16px;
  border: 1px solid rgba(56, 189, 248, 0.25);
  box-shadow: 0 4px 10px rgba(37, 99, 235, 0.08);
}

.stat-num {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.1;
  font-family: 'Plus Jakarta Sans', sans-serif;
  letter-spacing: -0.5px;
}

.stat-item:nth-child(1) .stat-num {
  color: var(--primary);
}
.stat-item:nth-child(2) .stat-num {
  color: #059669;
}
.stat-item:nth-child(3) .stat-num {
  color: #7c3aed;
}

.stat-label {
  font-size: 0.85rem;
  color: var(--muted);
  margin-top: 3px;
}

/* ================= CARDS & GRIDS CHUẨN UNICA ================= */
.section-title {
  font-size: 2rem;
  font-weight: 800;
  color: var(--dark);
  letter-spacing: -0.5px;
  margin-bottom: 8px;
}

.section-subtitle {
  color: var(--muted);
  font-size: 1.05rem;
  margin-bottom: 32px;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 28px;
  margin-bottom: 50px;
}

.card {
  background: var(--white);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  display: flex;
  flex-direction: column;
  position: relative;
}

.card:hover {
  transform: translateY(-6px);
  box-shadow: 0 16px 32px -6px rgba(15, 23, 42, 0.12);
  border-color: var(--text-muted);
}

.card-img-wrapper {
  position: relative;
  overflow: hidden;
  height: 200px;
}

.card-img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.4s ease;
}

.card:hover .card-img {
  transform: scale(1.05);
}

/* Nhãn Unica */
.badge-container {
  position: absolute;
  top: 12px;
  left: 12px;
  display: flex;
  gap: 8px;
  z-index: 2;
}

.card-badge-hot {
  background: linear-gradient(135deg, #ea580c 0%, #dc2626 100%);
  color: var(--text-on-primary);
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 800;
  box-shadow: 0 2px 6px rgba(220, 38, 38, 0.4);
}

.card-badge-discount {
  background: #f59e0b;
  color: #78350f;
  padding: 4px 8px;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 800;
}

.card-body {
  padding: 20px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.card-teacher {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 8px;
}

.card-teacher img {
  width: 22px;
  height: 22px;
  border-radius: 50%;
}

.card-title {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--dark);
  margin-bottom: 8px;
  line-height: 1.4;
}

.card-desc {
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 14px;
  flex: 1;
  line-height: 1.6;
}

.card-rating-line {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
  font-size: 0.85rem;
}

.stars {
  color: var(--star-color);
  letter-spacing: 1px;
}

.rating-score {
  font-weight: 700;
  color: var(--slate);
}

.rating-count {
  color: var(--muted);
}

.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 14px;
  border-top: 1px solid var(--border);
}

.price-current {
  font-size: 1.45rem;
  font-weight: 800;
  color: #dc2626;
}

.price-original {
  font-size: 0.9rem;
  color: var(--text-muted);
  text-decoration: line-through;
  margin-left: 6px;
}

/* ================= PHÒNG HỌC TẬP TRUNG (CINEMA LMS) ================= */
.classroom-layout {
  display: grid;
  grid-template-columns: 1fr 340px;
  height: calc(100vh - 64px);
  height: calc(100dvh - 64px);
  background: var(--cinema-bg);
  color: #f8fafc;
  overflow: hidden;
}

.classroom-topbar {
  height: 64px;
  background: var(--cinema-surface);
  border-bottom: 1px solid var(--cinema-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 20px;
  padding-top: env(safe-area-inset-top, 0px);
  padding-left: max(16px, env(safe-area-inset-left, 0px));
  padding-right: max(16px, env(safe-area-inset-right, 0px));
  color: var(--text-on-primary);
  z-index: 100;
  gap: 12px;
}

.topbar-left-cluster {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
  flex: 1;
}

.btn-topbar-back {
  padding: 6px 12px;
  font-size: 0.85rem;
  border-color: var(--border-color);
  color: var(--text-secondary);
  background: var(--bg-surface-soft);
  min-height: 38px;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  flex-shrink: 0;
  border-radius: 8px;
}

.topbar-titles {
  min-width: 0;
  overflow: hidden;
}

.top-course-name {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.top-lesson-name {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-main);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.topbar-progress-pill {
  background: rgba(37, 99, 235, 0.2);
  border: 1px solid rgba(56, 189, 248, 0.35);
  color: #38bdf8;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: 20px;
  font-family: 'JetBrains Mono', monospace;
  white-space: nowrap;
  flex-shrink: 0;
}

.topbar-right-cluster {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-shrink: 0;
}

.viewer-area {
  position: relative;
  display: flex;
  flex-direction: column;
  height: 100%;
  overflow-y: auto;
  scroll-behavior: smooth;
  background: #000000;
}

.lesson-frame-container {
  flex-shrink: 0;
  width: 100%;
  height: calc(100vh - 128px);
  height: calc(100dvh - 128px);
  min-height: 480px;
  position: relative;
  user-select: none;
  -webkit-user-select: none;
}

@media (max-width: 992px) {
  .lesson-frame-container {
    width: 100%;
    aspect-ratio: 16 / 9;
    height: auto;
    max-height: 54vh;
    max-height: 54dvh;
    min-height: 220px;
  }
}

.lesson-iframe {
  width: 100%;
  height: 100%;
  border: none;
  display: block;
}

/* Watermark Chống Quay Màn Hình */
.watermark-overlay {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  pointer-events: none;
  z-index: 50;
  overflow: hidden;
}

.watermark-text {
  position: absolute;
  font-family: monospace;
  font-size: 13px;
  color: rgba(255, 255, 255, 0.08);
  user-select: none;
  white-space: nowrap;
  transform: rotate(-15deg);
  transition: all 4s ease-in-out;
}

/* Sidebar Danh Mục Bài Học */
.syllabus-sidebar {
  background: var(--cinema-surface);
  border-left: 1px solid var(--cinema-border);
  display: flex;
  flex-direction: column;
  height: 100%;
  overflow: hidden;
}

.syllabus-header {
  padding: 20px;
  border-bottom: 1px solid var(--cinema-border);
}

.syllabus-list {
  flex: 1;
  overflow-y: auto;
  padding: 12px;
}

.syllabus-list::-webkit-scrollbar {
  width: 6px;
}
.syllabus-list::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.15);
  border-radius: 3px;
}

.syllabus-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  border-radius: var(--radius-sm);
  margin-bottom: 8px;
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.2s;
  color: var(--text-muted);
}

.syllabus-item:hover {
  background: rgba(255, 255, 255, 0.08);
  color: #f8fafc;
}

.syllabus-item.active {
  background: rgba(37, 99, 235, 0.15);
  border-color: rgba(56, 189, 248, 0.5);
  color: #38bdf8;
  font-weight: 700;
}

.syllabus-item.locked {
  opacity: 0.5;
  cursor: not-allowed;
}

.syllabus-number {
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.08);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  font-weight: 700;
}

.syllabus-item.active .syllabus-number {
  background: var(--primary);
  color: var(--text-on-primary);
}

/* Toast Thông Báo Bản Quyền */
.security-toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: rgba(15, 23, 42, 0.95);
  border: 1px solid rgba(239, 68, 68, 0.5);
  color: #fecaca;
  padding: 12px 24px;
  border-radius: 30px;
  font-size: 0.9rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 10px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
  z-index: 99999;
  opacity: 0;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  pointer-events: none;
}

.security-toast.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* Paywall Khóa Bài */
.paywall-container {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(10, 15, 29, 0.95);
  backdrop-filter: blur(16px);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 32px;
  z-index: 40;
}

/* ================= TESTIMONIALS (CẢM NHẬN HỌC VIÊN) ================= */
.testimonials-section {
  padding: 60px 0 20px;
}

.testimonial-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 24px;
}

.testimonial-card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 26px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  transition: transform 0.2s;
}

.testimonial-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.testimonial-quote {
  font-size: 0.95rem;
  color: var(--slate);
  line-height: 1.6;
  margin-bottom: 20px;
  position: relative;
}

.testimonial-author {
  display: flex;
  align-items: center;
  gap: 12px;
  border-top: 1px solid var(--border);
  padding-top: 14px;
}

.author-avatar {
  width: 44px;
  height: 44px;
  border-radius: 50%;
  object-fit: cover;
  border: 2px solid var(--primary-light);
}

.author-info h4 {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--dark);
}

.author-info p {
  font-size: 0.8rem;
  color: var(--muted);
}

.score-badge {
  background: var(--secondary-light);
  color: #059669;
  font-weight: 800;
  font-size: 0.75rem;
  padding: 2px 8px;
  border-radius: 4px;
  margin-left: auto;
}

/* ================= CTA BANNER CHỐT ĐƠN ================= */
.cta-banner {
  background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 60%, #38bdf8 100%);
  color: var(--text-on-primary);
  border-radius: var(--radius-lg);
  padding: 50px 36px;
  text-align: center;
  margin: 70px 0 40px;
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
}

.cta-banner h2 {
  font-size: 2.2rem;
  font-weight: 800;
  margin-bottom: 12px;
}

.cta-banner p {
  font-size: 1.1rem;
  opacity: 0.9;
  max-width: 600px;
  margin: 0 auto 28px;
}

/* ================= FOOTER ================= */
.footer {
  background: var(--white);
  border-top: 1px solid var(--border);
  padding: 48px 0 24px;
  margin-top: 80px;
  text-align: center;
  color: var(--muted);
  font-size: 0.95rem;
}

/* ================= MOBILE NAVIGATION & DRAWER ================= */
.mobile-menu-btn {
  display: none;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 8px;
  cursor: pointer;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 5px;
  width: 44px;
  height: 44px;
  transition: all 0.2s;
}

.mobile-menu-btn span {
  display: block;
  width: 22px;
  height: 2.5px;
  background-color: var(--slate);
  border-radius: 2px;
  transition: all 0.2s;
}

.mobile-drawer-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(9, 13, 22, 0.6);
  backdrop-filter: blur(4px);
  z-index: 1100;
  opacity: 0;
  visibility: hidden;
  transition: all 0.3s ease;
}

.mobile-drawer-overlay.active {
  opacity: 1;
  visibility: visible;
}

.mobile-drawer {
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  width: 290px;
  max-width: 85vw;
  background: var(--white);
  z-index: 1200;
  box-shadow: var(--shadow-lg);
  display: flex;
  flex-direction: column;
  transform: translateX(-100%);
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

.mobile-drawer.active {
  transform: translateX(0);
}

.mobile-drawer-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border);
}

.mobile-drawer-close {
  background: var(--bg-surface-soft);
  border: none;
  border-radius: 50%;
  width: 44px;
  height: 44px;
  font-size: 1.2rem;
  color: var(--muted);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.2s;
}

.mobile-drawer-close:hover {
  background: var(--bg-surface-soft);
  color: var(--slate);
}

.mobile-drawer-nav {
  flex: 1;
  padding: 16px 12px;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.mobile-nav-link {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  font-size: 1rem;
  font-weight: 600;
  color: var(--slate);
  border-radius: 8px;
  transition: all 0.2s;
  min-height: 48px;
}

.mobile-nav-link:hover, .mobile-nav-link.active {
  background: var(--primary-light);
  color: var(--primary);
}

.mobile-drawer-footer {
  padding: 16px 20px;
  border-top: 1px solid var(--border);
  background: var(--bg-page);
}

/* ================= TOAST NOTIFICATION & QUICK COPY ================= */
.toast-notification {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: #1e293b;
  color: #ffffff;
  padding: 12px 24px;
  border-radius: 30px;
  font-size: 0.92rem;
  font-weight: 600;
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.35);
  display: flex;
  align-items: center;
  gap: 10px;
  z-index: 9999;
  opacity: 0;
  transition: all 0.3s cubic-bezier(0.16, 1, 0.3, 1);
  pointer-events: none;
  max-width: 90vw;
  text-align: center;
}

.toast-notification.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

.btn-copy {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 6px 12px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--primary);
  background: var(--primary-light);
  border: 1px solid #bfdbfe;
  border-radius: 6px;
  cursor: pointer;
  min-height: 38px;
  transition: all 0.2s;
  user-select: none;
}

.btn-copy:hover {
  background: var(--primary-light);
}

.btn-copy:active {
  transform: scale(0.96);
}

/* ================= BỘ ĐIỀU HƯỚNG CẤP & LỚP (OLM-STYLE) ================= */
.grade-navigator-section {
  padding: 48px 0 20px;
}

.level-tabs {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  margin-bottom: 24px;
  overflow-x: auto;
  padding: 4px 6px 12px;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
  scroll-snap-type: x mandatory;
  overscroll-behavior-x: contain;
}
.level-tabs::-webkit-scrollbar {
  display: none;
}

.level-tab-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 12px 24px;
  border-radius: 30px;
  background: var(--white);
  border: 1.5px solid var(--border);
  color: var(--slate);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  box-shadow: var(--shadow-sm);
  white-space: nowrap;
  min-height: 48px;
  scroll-snap-align: start;
  flex-shrink: 0;
  touch-action: pan-x;
  user-select: none;
  -webkit-user-select: none;
}

.level-tab-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-1px);
}

.level-tab-btn:active {
  transform: scale(0.96);
}

.level-tab-btn.active {
  background: var(--primary-gradient);
  border-color: transparent;
  color: #ffffff;
  box-shadow: 0 4px 14px rgba(37, 99, 235, 0.35);
}

.grade-pills-wrap {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  margin-bottom: 32px;
  overflow-x: auto;
  padding: 4px 6px 14px;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
  scroll-snap-type: x mandatory;
  overscroll-behavior-x: contain;
}
.grade-pills-wrap::-webkit-scrollbar {
  display: none;
}

.grade-pill-btn {
  padding: 10px 20px;
  border-radius: 12px;
  background: var(--bg-surface-soft);
  border: 1.5px solid var(--border-color);
  color: var(--slate-600);
  font-weight: 700;
  font-size: 0.92rem;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  white-space: nowrap;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  scroll-snap-align: start;
  flex-shrink: 0;
  touch-action: pan-x;
  user-select: none;
  -webkit-user-select: none;
}

.grade-pill-btn:hover {
  background: var(--bg-surface-soft);
  color: var(--slate);
  transform: translateY(-1px);
}

.grade-pill-btn:active {
  transform: scale(0.96);
}

.grade-pill-btn.active {
  background: #1e293b;
  border-color: var(--slate);
  color: #ffffff;
  box-shadow: 0 4px 12px rgba(30, 41, 59, 0.25);
}

/* ── SIDEBAR DANH SÁCH LỚP (LUÔN MỞ) ── */
.sidebar-level-group {
  margin-bottom: 14px;
}

.sidebar-level-group:last-child {
  margin-bottom: 0;
}

.sidebar-level-title {
  font-size: 0.82rem;
  font-weight: 800;
  color: var(--text-muted, #64748b);
  text-transform: uppercase;
  letter-spacing: 0.6px;
  margin-bottom: 6px;
  padding: 0 6px;
  display: flex;
  align-items: center;
  gap: 6px;
}

.sidebar-grade-list {
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.sidebar-grade-btn {
  width: 100%;
  text-align: left;
  padding: 8px 12px;
  border-radius: 9px;
  border: 1px solid transparent;
  background: transparent;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-secondary, #475569);
  cursor: pointer;
  transition: all 0.15s ease;
  display: flex;
  align-items: center;
  gap: 6px;
}

.sidebar-grade-btn::before {
  content: "•";
  font-size: 1.1rem;
  color: var(--text-muted);
  line-height: 1;
}

.sidebar-grade-btn:hover {
  background: var(--bg-surface-soft);
  color: var(--slate);
}

.sidebar-grade-btn.active {
  background: #2563eb;
  color: #ffffff;
  font-weight: 700;
  box-shadow: 0 2px 8px rgba(37, 99, 235, 0.25);
}

.sidebar-grade-btn.active::before {
  color: #ffffff;
}

/* ── KHUNG CHƯƠNG BÀI HỌC (CHAPTER CARD BOX) ── */
.chapter-card-box {
  background: var(--bg-surface, #ffffff);
  border: 1px solid var(--border-color, #e2e8f0);
  border-radius: 20px;
  padding: 24px;
  box-shadow: 0 4px 20px -4px rgba(15, 23, 42, 0.05);
  transition: box-shadow 0.2s ease, border-color 0.2s ease;
  margin-bottom: 0;
}

.chapter-card-box:hover {
  border-color: var(--border);
  box-shadow: 0 8px 26px -6px rgba(15, 23, 42, 0.08);
}

.chapter-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  flex-wrap: wrap;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1.5px solid #f1f5f9;
}

.chapter-header-left {
  flex: 1;
  min-width: 260px;
}

.chapter-header-badges {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 8px;
}

.chapter-badge-tag {
  background: linear-gradient(135deg, #1e293b, #334155);
  color: #ffffff;
  font-size: 0.74rem;
  font-weight: 800;
  padding: 4px 10px;
  border-radius: 6px;
  letter-spacing: 0.5px;
}

.chapter-badge-branch {
  background: var(--primary-light);
  color: var(--primary);
  font-size: 0.76rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 6px;
  border: 1px solid #dbeafe;
}

.chapter-badge-count {
  font-size: 0.8rem;
  color: var(--text-muted, #64748b);
  font-weight: 600;
}

.chapter-title {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--text-main, #0f172a);
  margin: 4px 0 6px 0;
  line-height: 1.35;
}

.chapter-desc {
  font-size: 0.88rem;
  color: var(--text-secondary, #475569);
  margin: 0;
  line-height: 1.5;
}

.btn-chapter-link {
  font-size: 0.84rem;
  font-weight: 700;
  padding: 8px 16px;
  border-radius: 10px;
  white-space: nowrap;
}

/* ── DANH SÁCH BÀI HỌC TRONG CHƯƠNG ── */
.chapter-lessons-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.chapter-lesson-card {
  background: var(--bg-page);
  border: 1px solid var(--border-color);
  border-radius: 14px;
  padding: 16px 18px;
  transition: all 0.2s ease;
}

.chapter-lesson-card:hover {
  background: var(--bg-surface);
  border-color: var(--primary);
  box-shadow: 0 4px 16px -2px rgba(37, 99, 235, 0.08);
}

.lesson-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 14px;
  flex-wrap: wrap;
}

.lesson-left {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  flex: 1;
  min-width: 260px;
}

.lesson-step-badge {
  width: 32px;
  height: 32px;
  border-radius: 9px;
  background: #2563eb;
  color: #ffffff;
  font-weight: 800;
  font-size: 0.82rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.lesson-main-info {
  flex: 1;
  min-width: 0;
}

.lesson-title {
  font-size: 1.02rem;
  font-weight: 800;
  color: var(--text-main, #1e293b);
  margin: 0 0 4px 0;
  line-height: 1.35;
}

.lesson-hook {
  font-size: 0.84rem;
  color: var(--text-secondary, #475569);
  margin: 0 0 8px 0;
  line-height: 1.45;
}

.lesson-meta-chips {
  display: flex;
  align-items: center;
  gap: 6px;
  flex-wrap: wrap;
}

.badge-chip {
  font-size: 0.74rem;
  font-weight: 600;
  padding: 2px 8px;
  border-radius: 6px;
  background: var(--bg-surface-soft);
  color: var(--slate-600);
}

.badge-chip.badge-3d {
  background: var(--secondary-light);
  color: #059669;
  border: 1px solid #a7f3d0;
  font-weight: 700;
}

.badge-chip.badge-demo {
  background: #fef3c7;
  color: #b45309;
  font-weight: 700;
}

.lesson-right {
  display: flex;
  align-items: center;
  gap: 8px;
}

.btn-theory-overview {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  border-radius: 9px;
  background: linear-gradient(135deg, #2563eb, #0284c7);
  color: #ffffff !important;
  font-size: 0.84rem;
  font-weight: 800;
  text-decoration: none;
  box-shadow: 0 3px 10px rgba(37, 99, 235, 0.25);
  white-space: nowrap;
  transition: all 0.18s ease;
  flex-shrink: 0;
}

.btn-theory-overview:hover {
  transform: translateY(-1px);
  box-shadow: 0 5px 14px rgba(37, 99, 235, 0.35);
  color: #ffffff !important;
}

/* ── TẦNG 2: CÁC DẠNG TOÁN SGK MỚI & ĐGNL ── */
.lesson-dang-section {
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px dashed #cbd5e1;
}

.dang-section-title {
  font-size: 0.8rem;
  font-weight: 800;
  color: var(--text-main, #0f172a);
  margin-bottom: 8px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.dang-toan-grid {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.dang-item-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 8px 12px;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 9px;
  transition: all 0.15s ease;
}

.dang-item-row:hover {
  border-color: var(--primary);
  background: var(--primary-light);
}

.dang-item-left {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  flex: 1;
  min-width: 0;
}

.dang-icon {
  font-size: 1.1rem;
  flex-shrink: 0;
  line-height: 1.3;
}

.dang-info {
  min-width: 0;
}

.dang-title {
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--text-main, #1e293b);
  line-height: 1.35;
}

.dang-trap {
  font-size: 0.76rem;
  color: var(--trap-color, #fda4af);
  background: var(--trap-bg, rgba(244, 63, 94, 0.12));
  border: 1px solid var(--trap-border, rgba(244, 63, 94, 0.3));
  padding: 3px 8px;
  border-radius: 6px;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  margin-top: 4px;
  font-weight: 600;
  line-height: 1.35;
  transition: all 0.2s ease;
}

.dang-item-right {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-shrink: 0;
}

.dang-dur {
  font-size: 0.78rem;
  color: var(--text-muted);
  font-weight: 600;
  font-family: 'JetBrains Mono', monospace;
}

.btn-learn-dang {
  display: inline-flex;
  align-items: center;
  padding: 5px 12px;
  border-radius: 7px;
  background: var(--bg-surface);
  border: 1.5px solid #2563eb;
  color: var(--primary) !important;
  font-size: 0.8rem;
  font-weight: 700;
  text-decoration: none;
  white-space: nowrap;
  transition: all 0.15s ease;
}

.btn-learn-dang:hover {
  background: #2563eb;
  color: #ffffff !important;
}


.grade-topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 20px;
  margin-top: 20px;
}


.grade-topic-card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow-sm);
  transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
  overflow: hidden;
}

.grade-topic-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--primary);
}

.topic-header {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  margin-bottom: 12px;
}

.topic-icon-box {
  width: 48px;
  height: 48px;
  border-radius: 12px;
  background: var(--primary-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.6rem;
  flex-shrink: 0;
}

.topic-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--dark);
  line-height: 1.35;
  margin-bottom: 4px;
}

.topic-desc {
  font-size: 0.9rem;
  color: var(--muted);
  line-height: 1.5;
  margin-bottom: 16px;
}

.topic-badges {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.badge-3d {
  background: var(--secondary-light);
  color: #059669;
  border: 1px solid #a7f3d0;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 3px 8px;
  border-radius: 6px;
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.badge-lesson-count {
  background: var(--bg-page);
  color: var(--text-muted);
  border: 1px solid var(--border-color);
  font-size: 0.75rem;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: 6px;
}

.topic-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 14px;
  border-top: 1px solid #f1f5f9;
}

/* ============ BỐ CỤC SÀN HỌC LIỆU SỐ CHUẨN HOCLIEUBOTRO.NXGBD.VN ============ */
.grade-catalog-layout {
  display: grid;
  grid-template-columns: 260px minmax(0, 1fr);
  gap: 28px;
  align-items: start;
  margin-top: 24px;
  width: 100%;
  min-width: 0;
  max-width: 100%;
}

/* CỘT TRÁI: BỘ LỌC PHÂN MÔN */
.grade-sidebar-filter {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 18px;
  padding: 18px 16px;
  box-shadow: 0 4px 20px -4px rgba(15, 23, 42, 0.06);
  position: sticky;
  top: 90px;
  min-width: 0;
  max-width: 100%;
}

.grade-filter-title {
  font-size: 0.95rem;
  font-weight: 800;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border-color);
}

.grade-filter-list {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.grade-filter-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 14px;
  border-radius: 10px;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-secondary);
  background: transparent;
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  text-align: left;
  width: 100%;
}

.grade-filter-item:hover {
  background: var(--bg-surface-soft);
  color: var(--primary);
}

.grade-filter-item.active {
  background: var(--primary-light);
  border-color: rgba(37, 99, 235, 0.2);
  color: var(--primary);
  font-weight: 700;
}

.grade-filter-count {
  font-size: 0.75rem;
  background: rgba(148, 163, 184, 0.15);
  color: var(--text-muted);
  padding: 2px 8px;
  border-radius: 12px;
  font-weight: 700;
}

.grade-filter-item.active .grade-filter-count {
  background: var(--primary);
  color: #ffffff;
}

/* CỘT PHẢI: KỆ SÁCH & LƯỚI THẺ CHUYÊN ĐỀ */
.grade-books-container {
  min-width: 0;
}

.grade-catalog-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
  flex-wrap: wrap;
  gap: 12px;
}

.grade-catalog-title {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-main);
  margin: 0;
}

.grade-catalog-sub {
  font-size: 0.88rem;
  color: var(--text-muted);
  margin-top: 2px;
}

.btn-catalog-all {
  font-size: 0.85rem;
  font-weight: 700;
  padding: 8px 16px;
  border-radius: 20px;
}

/* KHU VỰC HIỂN THỊ CÁC CHƯƠNG & BÀI HỌC */
.grade-book-grid {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.grade-book-grid .chapter-card-box,
.chapter-card-box:last-child {
  margin-bottom: 0;
}


.grade-book-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 18px;
  overflow: hidden;
  box-shadow: 0 4px 16px -2px rgba(15, 23, 42, 0.05);
  transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
  position: relative;
}

.grade-book-card:hover {
  transform: translateY(-4px);
  border-color: var(--primary);
  box-shadow: 0 14px 28px -4px rgba(37, 99, 235, 0.12);
}

.grade-book-card:active {
  transform: scale(0.985);
}

/* BÌA CHUYÊN ĐỀ PHÍA TRÊN */
.book-card-cover {
  height: 130px;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  padding: 12px 14px;
}

.book-cover-bg-giai-tich {
  background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 60%, #38bdf8 100%);
}
.book-cover-bg-hinh-hoc {
  background: linear-gradient(135deg, #4c1d95 0%, #7c3aed 60%, #a855f7 100%);
}
.book-cover-bg-thong-ke {
  background: linear-gradient(135deg, #064e3b 0%, #059669 60%, #34d399 100%);
}
.book-cover-bg-van-dung-cao {
  background: linear-gradient(135deg, #7c2d12 0%, #ea580c 60%, #fb923c 100%);
}
.book-cover-bg-default {
  background: linear-gradient(135deg, #0f172a 0%, #334155 60%, #64748b 100%);
}

.book-cover-badge-left {
  position: absolute;
  top: 12px;
  left: 12px;
  background: var(--bg-frosted);
  backdrop-filter: blur(8px);
  color: var(--text-main);
  font-size: 0.72rem;
  font-weight: 800;
  padding: 3px 8px;
  border-radius: 6px;
  letter-spacing: 0.5px;
  box-shadow: 0 2px 6px rgba(0,0,0,0.15);
}

.book-cover-badge-right {
  position: absolute;
  top: 12px;
  right: 12px;
  background: rgba(15, 23, 42, 0.65);
  backdrop-filter: blur(8px);
  color: #ffffff;
  font-size: 0.72rem;
  font-weight: 700;
  padding: 3px 8px;
  border-radius: 6px;
  border: 1px solid rgba(255, 255, 255, 0.2);
}

.book-cover-icon {
  font-size: 3.2rem;
  filter: drop-shadow(0 4px 12px rgba(0, 0, 0, 0.3));
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

.grade-book-card:hover .book-cover-icon {
  transform: scale(1.12);
}

/* THÂN THẺ */
.book-card-body {
  padding: 18px 20px;
  display: flex;
  flex-direction: column;
  flex: 1;
  justify-content: space-between;
}

.book-card-title {
  font-size: 1.08rem;
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.35;
  margin-bottom: 6px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.book-card-desc {
  font-size: 0.82rem;
  color: var(--text-muted);
  line-height: 1.5;
  margin-bottom: 14px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.book-card-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.75rem;
  color: var(--muted);
  font-weight: 600;
  margin-bottom: 14px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border-color);
}

.book-card-btn {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 16px;
  border-radius: 10px;
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 700;
  font-size: 0.88rem;
  border: 1px solid rgba(37, 99, 235, 0.2);
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.grade-book-card:hover .book-card-btn {
  background: var(--primary);
  color: #ffffff;
  border-color: var(--primary);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.25);
}

/* RESPONSIVE TRÊN MOBILE VÀ TABLET */
@media (max-width: 900px) {
  .grade-catalog-layout {
    grid-template-columns: 100%;
    gap: 16px;
    width: 100%;
    min-width: 0;
    max-width: 100%;
  }
  .grade-sidebar-filter {
    position: static;
    padding: 12px 14px;
    border-radius: 14px;
    width: 100%;
    min-width: 0;
    max-width: 100%;
    overflow: hidden;
    box-sizing: border-box;
  }
  .grade-filter-title {
    margin-bottom: 8px;
    padding-bottom: 6px;
    font-size: 0.88rem;
  }
  .grade-filter-list {
    flex-direction: row;
    overflow-x: auto;
    padding-bottom: 6px;
    scrollbar-width: none;
    -webkit-overflow-scrolling: touch;
    gap: 8px;
    width: 100%;
    min-width: 0;
    max-width: 100%;
  }
  .grade-filter-list::-webkit-scrollbar {
    display: none;
  }
  .grade-filter-item {
    white-space: nowrap;
    width: auto;
    padding: 7px 12px;
    font-size: 0.82rem;
    flex-shrink: 0;
  }
  .grade-books-container {
    width: 100%;
    min-width: 0;
    max-width: 100%;
    box-sizing: border-box;
  }
  .grade-catalog-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 10px;
    width: 100%;
    min-width: 0;
    max-width: 100%;
  }
  .btn-catalog-all {
    width: 100%;
    text-align: center;
    justify-content: center;
    box-sizing: border-box;
  }
  .grade-catalog-title {
    font-size: 1.15rem;
    word-break: break-word;
  }
  .grade-book-grid {
    grid-template-columns: 1fr;
    gap: 14px;
    width: 100%;
    min-width: 0;
    max-width: 100%;
  }
  .grade-book-card {
    width: 100%;
    min-width: 0;
    max-width: 100%;
    box-sizing: border-box;
  }
}

@media (max-width: 640px) {
  .level-tabs,
  .grade-pills-wrap {
    justify-content: flex-start;
    padding-left: 12px;
    padding-right: 12px;
    width: 100%;
    max-width: 100%;
    box-sizing: border-box;
  }
  .lesson-card-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 10px;
  }
  .lesson-left {
    min-width: 100%;
    width: 100%;
  }
  .lesson-right {
    width: 100%;
  }
  .btn-theory-overview {
    width: 100%;
    justify-content: center;
  }
  .dang-item-row {
    flex-direction: column;
    align-items: flex-start;
    gap: 8px;
    padding: 10px 12px;
  }
  .dang-item-left {
    width: 100%;
  }
  .dang-item-right {
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: 8px;
    border-top: 1px dashed #e2e8f0;
  }
  .btn-learn-dang {
    flex: 1;
    justify-content: center;
    max-width: 160px;
  }
}

@media (max-width: 540px) {
  .grade-book-grid {
    grid-template-columns: 1fr;
  }
  .book-card-cover {
    height: 110px;
  }
  .book-cover-icon {
    font-size: 2.6rem;
  }
}

/* ============ BẢN ĐỒ CHƯƠNG HỌC TUẦN TỰ CHO NGƯỜI MẤT GỐC (SEQUENTIAL CHAPTER MAP) ============ */
.chapter-sequence-list {
  display: flex;
  flex-direction: column;
  gap: 24px;
  margin-top: 20px;
}

.chapter-card-box {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 24px 28px;
  box-shadow: 0 4px 16px -2px rgba(15, 23, 42, 0.05);
  transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  position: relative;
  overflow: hidden;
}

.chapter-card-box:hover {
  border-color: var(--primary);
  box-shadow: 0 10px 24px -4px rgba(37, 99, 235, 0.09);
}

.chapter-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  flex-wrap: wrap;
  margin-bottom: 16px;
  border-bottom: 1px solid #f1f5f9;
  padding-bottom: 16px;
}

.chapter-badges {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 8px;
}

.chapter-badge-num {
  background: var(--primary-light);
  color: var(--primary-dark);
  font-size: 0.8rem;
  font-weight: 800;
  padding: 4px 10px;
  border-radius: 6px;
  letter-spacing: 0.5px;
}

.chapter-badge-branch {
  background: var(--bg-page);
  color: var(--slate-600);
  font-size: 0.78rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 6px;
  border: 1px solid var(--border-color);
}

.chapter-badge-count {
  background: #ecfeff;
  color: #0891b2;
  font-size: 0.78rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 6px;
  border: 1px solid #a5f3fc;
}

.chapter-title {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--dark);
  margin: 0 0 6px 0;
  line-height: 1.35;
}

.chapter-desc {
  font-size: 0.92rem;
  color: var(--muted);
  line-height: 1.55;
  margin: 0;
}

.chapter-tip-box {
  background: var(--accent-amber-light);
  border: 1px solid #fde68a;
  border-radius: 10px;
  padding: 10px 14px;
  font-size: 0.86rem;
  color: #92400e;
  display: flex;
  align-items: flex-start;
  gap: 10px;
  margin-bottom: 16px;
  line-height: 1.45;
}

.chapter-lesson-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.chapter-lesson-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  padding: 12px 16px;
  background: var(--bg-page);
  border-radius: 10px;
  border: 1px solid #f1f5f9;
  transition: all 0.2s ease;
}

.chapter-lesson-row:hover {
  background: var(--secondary-light);
  border-color: var(--secondary);
  transform: translateX(4px);
}

.lesson-left-info {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
  flex: 1;
}

.lesson-step-num {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: #e0e7ff;
  color: #3730a3;
  font-size: 0.78rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.lesson-name-and-hook {
  min-width: 0;
}

.lesson-row-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--slate);
  margin-bottom: 2px;
}

.lesson-row-hook {
  font-size: 0.82rem;
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.lesson-row-badges {
  display: flex;
  align-items: center;
  gap: 6px;
  margin-top: 4px;
}

.lesson-right-actions {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
}

@media (max-width: 768px) {
  .chapter-card-box {
    padding: 18px 14px;
    border-radius: 14px;
  }
  .chapter-card-header {
    flex-direction: column;
    align-items: stretch;
    gap: 12px;
    padding-bottom: 12px;
  }
  .chapter-title {
    font-size: 1.15rem;
    line-height: 1.35;
  }
  .chapter-tip-box {
    padding: 8px 12px;
    font-size: 0.82rem;
  }
  .chapter-lesson-row {
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
    padding: 10px 12px;
    gap: 10px;
    border-radius: 10px;
  }
  .lesson-left-info {
    flex: 1;
    min-width: 0;
  }
  .lesson-step-num {
    width: 28px;
    height: 28px;
    min-width: 28px;
    font-size: 0.78rem;
  }
  .lesson-row-title {
    font-size: 0.88rem;
    font-weight: 700;
  }
  .lesson-row-hook {
    font-size: 0.76rem;
  }
  .lesson-right-actions {
    flex-shrink: 0;
    width: auto;
  }
  .lesson-right-actions .btn {
    padding: 6px 12px !important;
    font-size: 0.8rem !important;
    border-radius: 6px;
  }
}

@media (max-width: 480px) {
  .chapter-lesson-row {
    flex-direction: column;
    align-items: flex-start;
    gap: 8px;
  }
  .lesson-right-actions {
    width: 100%;
    display: flex;
    justify-content: flex-end;
  }
  .lesson-right-actions .btn {
    width: 100%;
    justify-content: center;
    text-align: center;
  }
}

/* ================= ĐẤU TRƯỜNG TOÁN HỌC OLM-STYLE (ARENA BATTLE) ================= */
.arena-section {
  background: linear-gradient(180deg, #090d16 0%, #0f172a 100%);
  border-radius: 20px;
  padding: 44px 32px;
  color: #ffffff;
  margin: 60px auto 40px;
  box-shadow: 0 20px 40px -15px rgba(0, 0, 0, 0.4);
  position: relative;
  overflow: hidden;
  border: 1px solid #1e293b;
}

.arena-header {
  text-align: center;
  margin-bottom: 32px;
}

.arena-badge-pill {
  background: rgba(245, 158, 11, 0.15);
  color: #f59e0b;
  border: 1px solid rgba(245, 158, 11, 0.3);
  padding: 4px 14px;
  border-radius: 20px;
  font-size: 0.82rem;
  font-weight: 800;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  letter-spacing: 0.5px;
  margin-bottom: 10px;
}

.arena-title {
  font-size: 2.1rem;
  font-weight: 800;
  background: linear-gradient(135deg, #ffffff 0%, #38bdf8 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  margin-bottom: 8px;
}

.arena-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr;
  gap: 28px;
  align-items: start;
}

.arena-battle-card {
  background: #131b2e;
  border: 1px solid #1e293b;
  border-radius: 16px;
  padding: 24px;
  box-shadow: var(--shadow);
  position: relative;
}

.arena-hud {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
  background: rgba(255, 255, 255, 0.04);
  padding: 10px 16px;
  border-radius: 10px;
  border: 1px solid rgba(255, 255, 255, 0.08);
}

.arena-score-box {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.95rem;
}

.arena-combo-badge {
  background: linear-gradient(135deg, #ea580c 0%, #dc2626 100%);
  color: #ffffff;
  padding: 2px 8px;
  border-radius: 6px;
  font-weight: 800;
  font-size: 0.8rem;
  animation: pulse 1.2s infinite;
}

.arena-timer-container {
  margin-bottom: 18px;
}

.arena-timer-bar {
  height: 8px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 4px;
  overflow: hidden;
}

.arena-timer-fill {
  height: 100%;
  width: 100%;
  background: #38bdf8;
  transition: width 0.1s linear, background-color 0.3s;
}

.arena-question-box {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 12px;
  padding: 20px;
  text-align: center;
  font-size: 1.15rem;
  font-weight: 700;
  line-height: 1.5;
  color: #f8fafc;
  min-height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 20px;
}

.arena-options-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.arena-opt-btn {
  background: #1e293b;
  border: 1.5px solid #334155;
  color: #f1f5f9;
  padding: 14px 16px;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  min-height: 52px;
  text-align: center;
}

.arena-opt-btn:hover {
  background: #2563eb;
  border-color: var(--primary);
  color: #ffffff;
  transform: translateY(-2px);
}

.arena-opt-btn.correct-flash {
  background: #059669 !important;
  border-color: #10b981 !important;
}

.arena-opt-btn.wrong-flash {
  background: #dc2626 !important;
  border-color: #ef4444 !important;
}

/* Bảng Vàng Vinh Danh Leaderboard */
.arena-leaderboard-card {
  background: #131b2e;
  border: 1px solid #1e293b;
  border-radius: 16px;
  padding: 24px;
}

.leaderboard-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 1.1rem;
  font-weight: 800;
  color: #f8fafc;
  margin-bottom: 16px;
  padding-bottom: 12px;
  border-bottom: 1px solid #1e293b;
}

.leaderboard-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.leaderboard-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 14px;
  background: rgba(255, 255, 255, 0.03);
  border-radius: 8px;
  border: 1px solid transparent;
  transition: all 0.2s;
}

.leaderboard-item:hover {
  background: rgba(255, 255, 255, 0.06);
}

.leaderboard-item.rank-1 {
  background: rgba(245, 158, 11, 0.12);
  border-color: rgba(245, 158, 11, 0.3);
}

.leaderboard-rank {
  width: 28px;
  font-size: 1.1rem;
  font-weight: 800;
  text-align: center;
}

.leaderboard-user {
  display: flex;
  align-items: center;
  gap: 10px;
  flex: 1;
  min-width: 0;
  margin: 0 10px;
}

.leaderboard-avatar {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1px solid rgba(255, 255, 255, 0.2);
}

.leaderboard-name {
  font-size: 0.9rem;
  font-weight: 700;
  color: #f8fafc;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.leaderboard-sub {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.leaderboard-pts {
  font-weight: 800;
  color: #38bdf8;
  font-size: 0.95rem;
}

/* ================= RESPONSIVE (MOBILE-FIRST POLISH) ================= */
html, body {
  max-width: 100vw;
  overflow-x: clip;
}

@media (max-width: 1024px) {
  .header-inner {
    justify-content: space-between;
  }
  .nav-links {
    display: none;
  }
  .mobile-menu-btn {
    display: flex;
  }
  .classroom-layout {
    display: flex;
    flex-direction: column;
    height: auto;
    min-height: calc(100vh - 60px);
    min-height: calc(100dvh - 60px);
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
  }
  body.in-classroom {
    overflow-y: auto !important;
    height: auto !important;
  }
  .viewer-area {
    height: auto;
    min-height: auto;
    overflow: visible;
  }
  .syllabus-sidebar {
    height: auto;
    border-left: none;
    border-top: 1px solid var(--cinema-border);
  }
  .hero-grid {
    grid-template-columns: 1fr;
    text-align: center;
  }
  .hero-actions {
    justify-content: center;
    flex-wrap: wrap;
  }
  .hero-trust {
    justify-content: center;
  }
  .stats-bar {
    grid-template-columns: repeat(3, 1fr);
    margin-top: 30px;
    gap: 16px;
    padding: 20px;
  }
}

@media (max-width: 768px) {
  .container {
    padding: 0 16px;
  }
  .header-inner {
    height: 58px;
    gap: 8px;
  }
  .logo {
    font-size: 1.05rem;
    gap: 8px;
  }
  .logo-icon {
    font-size: 1.3rem;
  }
  .logo-text {
    font-size: 1.02rem;
    white-space: nowrap;
  }
  .header-auth-desktop,
  .header-qr-pill {
    display: none !important;
  }
  .lang-switcher-btn {
    padding: 6px 12px;
    font-size: 0.82rem;
    min-height: 44px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }

  .hero {
    padding: 24px 0 32px;
  }
  .hero-title {
    font-size: 1.8rem;
    line-height: 1.25;
  }
  .hero-desc {
    font-size: 0.96rem;
  }

  /* Lưới các thẻ bài học & nội dung xếp 1 cột gọn gàng */
  .grid-3,
  .course-grid,
  .testimonial-grid,
  .grade-topic-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  /* 3 chỉ số uy tín - bố trí 3 thẻ ngang xếp dọc cân đối 100%, không bị lẻ mục */
  .stats-bar {
    display: flex;
    flex-direction: column;
    padding: 14px 16px;
    gap: 10px;
    margin-top: 20px;
    border-radius: 16px;
    box-shadow: 0 4px 16px rgba(15, 23, 42, 0.06);
  }
  .stat-item {
    display: flex;
    align-items: center;
    justify-content: flex-start;
    padding: 10px 14px;
    gap: 14px;
    background: var(--bg-surface-soft);
    border: 1px solid var(--border-color);
    border-radius: 12px;
  }
  .stat-icon {
    width: 44px;
    height: 44px;
    min-width: 44px;
    font-size: 1.4rem;
    border-radius: 10px;
  }
  .stat-num {
    font-size: 1.35rem;
    font-weight: 800;
    line-height: 1.1;
  }
  .stat-label {
    font-size: 0.82rem;
    color: var(--muted);
    white-space: nowrap;
    margin-top: 2px;
  }

  /* Bộ điều hướng Cấp & Lớp: vuốt ngón tay mượt mà chuẩn mobile app */
  .grade-navigator-section {
    padding: 24px 0 16px;
  }
  .level-tabs {
    justify-content: flex-start;
    padding: 6px 16px 12px;
    margin-left: -16px;
    margin-right: -16px;
    gap: 10px;
    mask-image: linear-gradient(to right, black 85%, transparent 100%);
    -webkit-mask-image: linear-gradient(to right, black 85%, transparent 100%);
  }
  .level-tab-btn {
    padding: 8px 18px;
    font-size: 0.88rem;
    min-height: 44px;
    flex-shrink: 0;
  }
  .grade-pills-wrap {
    justify-content: flex-start;
    padding: 6px 16px 14px;
    margin-left: -16px;
    margin-right: -16px;
    gap: 8px;
    margin-bottom: 20px;
    mask-image: linear-gradient(to right, black 85%, transparent 100%);
    -webkit-mask-image: linear-gradient(to right, black 85%, transparent 100%);
  }
  .grade-pill-btn {
    padding: 8px 16px;
    font-size: 0.88rem;
    min-height: 42px;
    flex-shrink: 0;
  }

  /* Kệ khóa học hiện đại */
  .shelf-section {
    margin: 28px 0;
    padding: 18px 14px;
    border-radius: var(--radius);
  }
  .shelf-header {
    margin-bottom: 14px;
  }
  .shelf-title {
    font-size: 1.35rem;
  }
  .shelf-action-link {
    font-size: 0.88rem;
    padding: 4px 8px;
  }

  /* Thẻ bài học */
  .grade-topic-card {
    padding: 18px 14px;
  }
  .topic-footer {
    flex-direction: column;
    align-items: stretch;
    gap: 8px;
  }
  .topic-footer .btn {
    width: 100%;
    justify-content: center;
  }

  /* Đấu trường toán học OLM */
  .arena-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }
  .arena-section {
    padding: 24px 14px;
    margin: 30px auto 20px;
    border-radius: 14px;
  }
  .arena-title {
    font-size: 1.55rem;
  }
  .arena-battle-card {
    padding: 16px 14px;
  }
  .arena-options-grid {
    grid-template-columns: 1fr;
    gap: 10px;
  }
  .arena-opt-btn {
    padding: 12px 14px;
    font-size: 0.95rem;
  }

  /* Cảm nhận học viên */
  .testimonial-card {
    padding: 20px 16px;
  }

  /* Banner kêu gọi hành động & Footer */
  .cta-banner {
    padding: 28px 16px;
    border-radius: var(--radius);
  }
  .cta-banner h2 {
    font-size: 1.45rem;
  }
  .footer {
    margin-top: 40px;
    padding: 32px 0 20px;
  }
  .btn, .btn-copy {
    min-height: 44px;
    padding: 10px 16px;
  }
  .announcement-bar {
    font-size: 0.78rem;
    padding: 8px 12px;
    flex-direction: column;
    gap: 4px;
  }
  .announcement-badge {
    align-self: center;
  }

  /* Tối ưu phòng học trên mobile */
  .classroom-topbar {
    height: 52px;
    padding: 0 10px;
    flex-wrap: nowrap;
    gap: 8px;
  }
  .topbar-left-cluster {
    gap: 8px;
  }
  .topbar-titles {
    max-width: 140px;
  }
  .top-course-name {
    display: none;
  }
  .top-lesson-name {
    font-size: 0.85rem;
  }
  .topbar-progress-pill {
    display: none;
  }
  .topbar-right-cluster {
    gap: 6px;
  }
  .topbar-logo {
    display: none !important;
  }
  .btn-topbar-back {
    padding: 6px 10px;
    min-height: 36px;
    font-size: 0.8rem;
  }
  .btn-topbar-back .back-text {
    display: none;
  }
  .btn-cinema-action .action-btn-text {
    display: none;
  }
  .btn-cinema-action {
    padding: 6px 8px;
    min-height: 36px;
    min-width: 36px;
    justify-content: center;
  }
  .topbar-icon-btn {
    width: 36px;
    height: 36px;
    min-height: 36px;
    font-size: 0.8rem;
  }

  .classroom-layout {
    display: flex;
    flex-direction: column;
    height: auto;
    min-height: calc(100vh - 52px);
    min-height: calc(100dvh - 52px);
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
  }
  .viewer-area {
    height: auto;
    min-height: auto;
    overflow: visible;
  }
  .lesson-frame-container {
    width: 100%;
    aspect-ratio: 16 / 9;
    height: auto;
    max-height: 48vh;
    max-height: 48dvh;
    min-height: 200px;
    position: sticky;
    top: 0;
    z-index: 25;
  }

  .lecture-controls-bar {
    padding: 10px 12px;
    flex-direction: column;
    gap: 10px;
  }
  .controls-nav-group {
    display: flex;
    gap: 6px;
    width: 100%;
  }
  .controls-nav-group .btn-lecture-nav {
    flex: 1;
    padding: 8px 6px;
    font-size: 0.78rem;
    min-height: 42px;
    border-radius: 8px;
    justify-content: center;
  }
  .controls-utility-group {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    gap: 8px;
  }
  .speed-label {
    display: none;
  }
  .speed-pill-group {
    padding: 2px;
  }
  .speed-selector-pill {
    padding: 3px 6px;
    font-size: 0.74rem;
    min-height: 26px;
  }
  .btn-quiz-jump {
    padding: 6px 10px;
    font-size: 0.76rem;
    min-height: 32px;
  }

  .lesson-quiz-section {
    padding: 20px 12px 48px;
  }
  .lesson-quiz-card {
    padding: 16px 12px;
    border-radius: 14px;
  }
  .quiz-header-bar {
    margin-bottom: 14px;
    gap: 8px;
  }
  .quiz-badge-pill {
    font-size: 0.76rem;
    padding: 4px 10px;
  }
  .quiz-score-pill {
    font-size: 0.82rem;
    padding: 3px 8px;
  }
  .quiz-question-box {
    font-size: 0.95rem;
    padding: 14px 14px;
    line-height: 1.5;
    margin-bottom: 14px;
  }
  .quiz-options-grid {
    grid-template-columns: 1fr;
    gap: 8px;
  }
  .quiz-opt-btn {
    min-height: 46px;
    padding: 10px 12px;
    font-size: 0.88rem;
  }

  .syllabus-header {
    padding: 14px 16px;
  }
  .syllabus-item {
    padding: 12px 14px;
    min-height: 52px;
  }

  /* Course Explorer K12 */
  .k12-explorer-wrap {
    padding: 0 12px;
  }
  .k12-explorer-layout {
    grid-template-columns: 1fr;
  }
  .k12-sidebar {
    position: static;
    max-height: none;
    padding: 12px;
  }
  .k12-content-panel {
    padding: 14px 12px;
    min-height: auto;
  }
  .k12-overview-banner {
    padding: 14px 12px;
    margin-bottom: 16px;
  }
  .k12-overview-banner h2 {
    font-size: 1.25rem;
  }
  .k12-lesson-card {
    padding: 14px 12px;
  }
  .k12-video-row {
    flex-direction: column;
    align-items: stretch;
    gap: 8px;
    padding: 10px 10px;
  }
  .k12-video-row .vid-left {
    min-width: 0;
    width: 100%;
  }
  .k12-video-row .vid-right {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    gap: 10px;
  }
  .k12-video-row .vid-right .btn {
    flex: 1;
    justify-content: center;
    min-height: 40px;
    padding: 8px 12px;
    font-size: 0.82rem;
  }
}

@media (max-width: 480px) {
  .hero-title {
    font-size: 1.55rem;
  }
  .hero-subtitle {
    font-size: 0.92rem;
  }
  .course-card {
    border-radius: var(--radius);
  }
  .card-body {
    padding: 16px 14px;
  }
  .btn {
    width: 100%;
    justify-content: center;
    min-height: 44px;
  }
  .hero-actions {
    flex-direction: column;
    width: 100%;
    gap: 10px;
  }
  .hero-actions .btn {
    width: 100%;
    min-height: 48px;
  }
  .topbar-titles {
    max-width: 120px;
  }
  .controls-nav-group .btn-lecture-nav {
    font-size: 0.75rem;
    padding: 6px 4px;
  }
  .level-tab-btn {
    padding: 8px 14px;
    font-size: 0.84rem;
    min-height: 44px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }
  .grade-pill-btn {
    padding: 8px 13px;
    font-size: 0.84rem;
    min-height: 44px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }
}

@media (max-width: 380px) {
  .logo-text {
    font-size: 0.92rem;
  }
  .lang-switcher-btn {
    padding: 6px 10px;
    font-size: 0.78rem;
    min-height: 40px;
  }
  .level-tab-btn {
    padding: 7px 12px;
    font-size: 0.8rem;
    min-height: 42px;
  }
  .grade-pill-btn {
    padding: 7px 11px;
    font-size: 0.8rem;
    min-height: 42px;
  }
}

/* Chế độ xoay ngang điện thoại (Landscape Mobile) */
@media (max-height: 500px) and (orientation: landscape) {
  .classroom-topbar {
    display: none;
  }
  .classroom-layout {
    grid-template-columns: 1fr;
    grid-template-rows: 1fr;
    height: 100vh;
    height: 100dvh;
  }
  .syllabus-sidebar {
    display: none;
  }
  .syllabus-sidebar.mobile-open {
    display: flex;
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    width: 320px;
    z-index: 1000;
  }
}

/* ================= EDTECH MICRO-ANIMATIONS ================= */
.reveal-fade-up {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.5s cubic-bezier(0.16, 1, 0.3, 1), transform 0.5s cubic-bezier(0.16, 1, 0.3, 1);
  will-change: opacity, transform;
}

.reveal-scale {
  opacity: 0;
  transform: scale(0.95);
  transition: opacity 0.5s cubic-bezier(0.16, 1, 0.3, 1), transform 0.5s cubic-bezier(0.16, 1, 0.3, 1);
  will-change: opacity, transform;
}

.reveal-fade-up.revealed,
.reveal-scale.revealed {
  opacity: 1;
  transform: translateY(0) scale(1);
}

/* Stagger delay classes */
.delay-100 { transition-delay: 100ms; }
.delay-200 { transition-delay: 200ms; }
.delay-300 { transition-delay: 300ms; }
.delay-400 { transition-delay: 400ms; }

/* Subtle pulse glow for primary CTA button */
@keyframes subtle-glow {
  0%, 100% {
    box-shadow: 0 4px 15px rgba(234, 88, 12, 0.35);
  }
  50% {
    box-shadow: 0 6px 24px rgba(234, 88, 12, 0.65);
  }
}

.btn-pulse {
  animation: subtle-glow 2.5s infinite ease-in-out;
}

/* Hiệu ứng nhịp số nhảy khi animate */
.stat-num.counting {
  color: var(--primary);
}

/* Tôn trọng người dùng không thích chuyển động */
@media (prefers-reduced-motion: reduce) {
  .reveal-fade-up,
  .reveal-scale {
    opacity: 1 !important;
    transform: none !important;
    transition: none !important;
  }
  .btn-pulse {
    animation: none !important;
  }
}

/* ================= HOMEPAGE CURATED SHELVES (FUSHIN-STYLE) ================= */
.shelf-section {
  margin: 50px 0;
  padding: 32px 28px;
  background: var(--bg-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.03);
}

.shelf-section.shelf-accent-12 {
  border-top: 4px solid #dc2626;
  background: linear-gradient(180deg, #fffafa 0%, #ffffff 120px);
}

.shelf-section.shelf-accent-11 {
  border-top: 4px solid #2563eb;
  background: linear-gradient(180deg, #f0f7ff 0%, #ffffff 120px);
}

.shelf-section.shelf-accent-10 {
  border-top: 4px solid #059669;
  background: linear-gradient(180deg, #f0fdf4 0%, #ffffff 120px);
}

.shelf-section.shelf-accent-thcs {
  border-top: 4px solid #ea580c;
  background: linear-gradient(180deg, #fff7ed 0%, #ffffff 120px);
}

.shelf-header {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  margin-bottom: 24px;
  flex-wrap: wrap;
  gap: 12px;
}

.shelf-title-wrap {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.shelf-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.78rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  padding: 3px 10px;
  border-radius: 20px;
  width: fit-content;
}

.shelf-badge.red { background: #fee2e2; color: #dc2626; }
.shelf-badge.blue { background: var(--primary-light); color: #2563eb; }
.shelf-badge.green { background: #dcfce7; color: #059669; }
.shelf-badge.orange { background: #ffedd5; color: #ea580c; }

.shelf-title {
  font-size: 1.65rem;
  font-weight: 800;
  color: var(--dark);
  letter-spacing: -0.5px;
}

.shelf-action-link {
  font-weight: 700;
  font-size: 0.95rem;
  color: var(--accent-orange);
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: all 0.2s;
  padding: 6px 12px;
  border-radius: 6px;
}
.shelf-action-link:hover {
  background: rgba(234, 88, 12, 0.08);
  transform: translateX(3px);
}

/* ================= K12 COURSE EXPLORER (MASTER - DETAIL 2 CỘT) ================= */
.k12-explorer-wrap {
  margin: 32px 0 60px;
}

.k12-search-container {
  margin-bottom: 24px;
  position: relative;
}

.k12-search-input {
  width: 100%;
  padding: 14px 20px 14px 48px;
  font-size: 1.05rem;
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius);
  background: var(--bg-surface);
  color: var(--text-main);
  outline: none;
  transition: all 0.2s;
  box-shadow: var(--shadow-sm);
}

.k12-search-input::placeholder {
  color: var(--text-muted);
}

.k12-search-input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.15);
}

.k12-search-icon {
  position: absolute;
  left: 18px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.2rem;
  color: var(--muted);
  pointer-events: none;
}

.k12-explorer-wrap {
  max-width: 1560px;
}

/* DẢI CHỌN LỚP NHANH TRÊN ĐẦU (TOUCH-FRIENDLY SCROLL) */
.k12-top-filters {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 24px;
  overflow-x: auto;
  padding: 6px 4px 12px;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
  scroll-snap-type: x mandatory;
  overscroll-behavior-x: contain;
}
.k12-top-filters::-webkit-scrollbar {
  display: none;
}

.k12-filter-pill {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 9px 18px;
  border-radius: 25px;
  border: 1.5px solid var(--border-color);
  background: var(--bg-surface);
  font-weight: 700;
  color: var(--text-secondary);
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  font-size: 0.9rem;
  min-height: 42px;
  scroll-snap-align: start;
  flex-shrink: 0;
  touch-action: pan-x;
  user-select: none;
  -webkit-user-select: none;
}

.k12-filter-pill:hover {
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-1px);
}

.k12-filter-pill:active {
  transform: scale(0.96);
}

.k12-filter-pill.active {
  background: var(--primary);
  color: #ffffff;
  border-color: var(--primary);
  box-shadow: 0 4px 14px rgba(37, 99, 235, 0.3);
}

.k12-explorer-layout {
  display: grid;
  grid-template-columns: 320px minmax(0, 1fr);
  gap: 28px;
  align-items: start;
}

/* CỘT TRÁI: CÂY DANH MỤC CỐ ĐỊNH (STICKY INDEPENDENT SCROLL) */
.k12-sidebar {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 16px;
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 84px;
  max-height: calc(100vh - 96px);
  max-height: calc(100dvh - 96px);
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
  overscroll-behavior-y: contain;
}
.k12-sidebar::-webkit-scrollbar {
  width: 5px;
}
.k12-sidebar::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

.k12-sidebar-title {
  font-size: 0.85rem;
  font-weight: 800;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 12px;
  padding: 0 6px;
}

.k12-grade-group {
  margin-bottom: 8px;
}

.k12-grade-btn {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 12px;
  border-radius: 8px;
  background: transparent;
  border: none;
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--slate);
  cursor: pointer;
  text-align: left;
  transition: all 0.15s;
}

.k12-grade-btn:hover {
  background: var(--bg-surface-soft);
  color: var(--primary);
}

.k12-grade-btn.active {
  background: var(--primary-light);
  color: var(--primary);
}

.k12-chapter-list {
  padding-left: 14px;
  border-left: 2px solid var(--border-color);
  margin: 6px 0 10px 12px;
}

.k12-chapter-btn {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 10px;
  border-radius: 6px;
  background: transparent;
  border: none;
  font-size: 0.86rem;
  font-weight: 600;
  color: var(--muted);
  cursor: pointer;
  text-align: left;
  transition: all 0.15s;
}

.k12-chapter-btn:hover {
  color: var(--text-main);
  background: var(--bg-surface-soft);
}

.k12-chapter-btn.active {
  color: #0284c7;
  background: var(--primary-light);
  font-weight: 700;
}

.k12-badge-count {
  font-size: 0.72rem;
  background: var(--border-color);
  color: var(--text-secondary);
  padding: 2px 7px;
  border-radius: 12px;
  font-weight: 700;
}

/* CỘT PHẢI: NỘI DUNG TƯƠNG ỨNG SỔ RA */
.k12-content-panel {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: clamp(20px, 2.4vw, 32px);
  box-shadow: var(--shadow-sm);
  min-height: 520px;
  min-width: 0;
}

.k12-breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.k12-breadcrumb a {
  color: var(--primary);
  font-weight: 600;
  cursor: pointer;
}

.k12-breadcrumb a:hover {
  text-decoration: underline;
}

.k12-overview-banner {
  background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 100%);
  color: var(--text-on-primary);
  padding: 24px;
  border-radius: var(--radius);
  margin-bottom: 28px;
}

.k12-overview-banner h2 {
  font-size: 1.6rem;
  font-weight: 800;
  margin-bottom: 8px;
}

.k12-lesson-card {
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 20px 22px;
  margin-bottom: 20px;
  background: var(--bg-surface);
  box-shadow: 0 2px 8px -2px rgba(15, 23, 42, 0.05);
  transition: transform 0.25s cubic-bezier(0.16, 1, 0.3, 1), box-shadow 0.25s cubic-bezier(0.16, 1, 0.3, 1), border-color 0.2s ease;
}

.k12-lesson-card:hover {
  border-color: var(--primary);
  box-shadow: 0 10px 24px -4px rgba(37, 99, 235, 0.10);
  transform: translateY(-2px);
}

.k12-lesson-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.k12-lesson-title {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.badge-3d-pill {
  background: var(--secondary-light);
  color: #059669;
  font-size: 0.75rem;
  font-weight: 800;
  padding: 3px 8px;
  border-radius: 6px;
}

.badge-demo-pill {
  background: var(--primary-light);
  color: var(--primary);
  font-size: 0.75rem;
  font-weight: 800;
  padding: 3px 8px;
  border-radius: 6px;
}

/* ================= K12 CHAPTER LESSONS QUICK GRID (2 CỘT CÂN ĐỐI ĐỀU & ĐẸP) ================= */
.k12-chapter-lesson-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 10px;
  margin-top: 14px;
  padding-top: 14px;
  border-top: 1px solid var(--border-color);
}

@media (max-width: 768px) {
  .k12-chapter-lesson-grid {
    grid-template-columns: 1fr;
    gap: 8px;
  }
}

.k12-chapter-lesson-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 14px;
  background: var(--bg-surface-soft);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  text-decoration: none;
}

.k12-chapter-lesson-item:hover {
  background: var(--bg-surface);
  border-color: var(--primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.1);
}

.k12-chapter-lesson-item:active {
  transform: scale(0.98);
}

.k12-chapter-lesson-item .lesson-chip-left {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
  flex: 1;
}

.k12-chapter-lesson-item .lesson-chip-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 800;
  font-size: 0.78rem;
  border-radius: 8px;
  flex-shrink: 0;
  border: 1px solid rgba(37, 99, 235, 0.15);
}

.k12-chapter-lesson-item .lesson-chip-name {
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--text-main);
  line-height: 1.35;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
  transition: color 0.15s ease;
}

.k12-chapter-lesson-item:hover .lesson-chip-name {
  color: var(--primary);
}

.k12-chapter-lesson-item .lesson-chip-right {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
}

.k12-chapter-lesson-item .lesson-chip-arrow {
  color: var(--text-muted);
  font-size: 0.9rem;
  font-weight: 700;
  transition: transform 0.2s ease, color 0.2s ease;
}

.k12-chapter-lesson-item:hover .lesson-chip-arrow {
  transform: translateX(3px);
  color: var(--primary);
}

/* SIDEBAR LESSON ITEM */
.k12-sidebar-lesson-item {
  padding: 6px 10px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.84rem;
  margin-bottom: 2px;
  transition: all 0.15s ease;
  background: transparent;
  color: var(--text-secondary);
  font-weight: 500;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

.k12-sidebar-lesson-item:hover {
  background: var(--bg-surface-soft);
  color: var(--text-main);
}

.k12-sidebar-lesson-item.active {
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 700;
}

.k12-sidebar-lesson-item .sidebar-lesson-name {
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 195px;
}

/* BỐ CỤC 2 CỘT PHÒNG HỌC STUDIO (LESSON VIEW) */
.k12-lesson-studio-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 340px;
  gap: 28px;
  align-items: start;
  width: 100%;
}

.k12-lesson-main {
  min-width: 0;
}

.k12-lesson-aside {
  position: sticky;
  top: 90px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.k12-companion-card {
  background: var(--bg-surface-soft);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 18px;
  box-shadow: var(--shadow-xs);
}

.k12-companion-title {
  font-size: 0.95rem;
  font-weight: 800;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 10px;
}

.k12-companion-body {
  font-size: 0.88rem;
  line-height: 1.6;
  color: var(--text-secondary);
}

/* THẺ VIDEO TẦNG 1 MỚI (XÓA BỎ NỀN ĐEN) */
.overview-video-card {
  background: linear-gradient(135deg, #f0fdfa 0%, #f0f9ff 50%, #eff6ff 100%);
  border: 1.5px solid #bfdbfe;
  border-radius: 16px;
  padding: 22px 24px;
  margin: 18px 0 24px;
  box-shadow: 0 10px 25px -5px rgba(37, 99, 235, 0.08), 0 4px 6px -2px rgba(37, 99, 235, 0.04);
  color: var(--text-main);
  position: relative;
  overflow: hidden;
  transition: all 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

.overview-video-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 16px 32px -6px rgba(37, 99, 235, 0.16);
  border-color: #60a5fa;
}

[data-theme="dark"] .overview-video-card {
  background: linear-gradient(135deg, #111827 0%, #172554 100%);
  border: 1.5px solid #2563eb;
  box-shadow: 0 10px 25px -5px rgba(37, 99, 235, 0.25);
  color: #f8fafc;
}

.overview-card-content {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 20px;
  align-items: center;
}

@media (max-width: 640px) {
  .overview-card-content {
    grid-template-columns: 1fr;
  }
}

.k12-video-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 10px;
  margin-top: 14px;
}

.k12-video-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 16px;
  background: var(--bg-surface-soft);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  font-size: 0.92rem;
  gap: 12px;
  flex-wrap: wrap;
  transition: all 0.2s;
}

.k12-video-row:hover {
  border-color: var(--primary);
  background: var(--bg-surface);
  transform: translateX(3px);
  box-shadow: var(--shadow-sm);
}

.k12-video-row.is-main {
  background: var(--primary-light);
  border-color: var(--border-color);
}

.k12-video-row .vid-left {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  color: var(--text-main);
  flex: 1;
  min-width: 220px;
}

.k12-trap-note {
  font-size: 0.82rem;
  color: var(--trap-color, #be123c);
  background: var(--trap-bg, rgba(225, 29, 72, 0.07));
  padding: 6px 12px;
  border-radius: 6px;
  margin-top: 6px;
  border: 1px solid var(--trap-border, rgba(225, 29, 72, 0.22));
  border-left: 3.5px solid var(--trap-color, #be123c);
  line-height: 1.4;
  font-weight: 500;
  transition: all 0.2s ease;
}

[data-theme="dark"] .k12-trap-note {
  background: var(--trap-bg, rgba(244, 63, 94, 0.12));
  color: var(--trap-color, #fda4af);
  border-color: var(--trap-border, rgba(244, 63, 94, 0.3));
  border-left-color: #fb7185;
}

@media (max-width: 1100px) {
  .k12-lesson-studio-layout {
    grid-template-columns: 1fr;
    gap: 20px;
  }
  .k12-lesson-aside {
    position: static;
  }
}

@media (max-width: 900px) {
  .k12-top-filters {
    position: sticky;
    top: 60px;
    z-index: 90;
    background: rgba(248, 250, 252, 0.94);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    padding: 8px 16px 12px;
    margin-left: -16px;
    margin-right: -16px;
    margin-bottom: 20px;
    border-bottom: 1px solid var(--border);
    mask-image: linear-gradient(to right, black 85%, transparent 100%);
    -webkit-mask-image: linear-gradient(to right, black 85%, transparent 100%);
  }
  [data-theme="dark"] .k12-top-filters {
    background: rgba(11, 15, 25, 0.94);
  }
  .k12-filter-pill {
    font-size: 0.85rem;
    padding: 8px 16px;
    min-height: 40px;
  }
  .k12-explorer-layout {
    display: flex;
    flex-direction: column;
    gap: 24px;
  }
  .k12-content-panel {
    order: 1; /* Ưu tiên nội dung bài học lên đầu */
    width: 100%;
  }
  .k12-sidebar {
    order: 2; /* Đặt mục lục sau, không đẩy nội dung xuống sâu */
    position: static;
    max-height: none;
    width: 100%;
  }
}

/* ================= EDTECH MODERN TOAST SYSTEM ================= */
.edtech-toast-container {
  position: fixed;
  top: 24px;
  right: 24px;
  z-index: 99999;
  display: flex;
  flex-direction: column;
  gap: 10px;
  pointer-events: none;
}

.edtech-toast {
  pointer-events: auto;
  display: flex;
  align-items: center;
  gap: 12px;
  background: rgba(15, 23, 42, 0.94);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  color: #ffffff;
  padding: 12px 18px;
  border-radius: 12px;
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.3), 0 0 0 1px rgba(255, 255, 255, 0.1);
  font-size: 0.92rem;
  font-weight: 600;
  max-width: 380px;
  transform: translateX(120%);
  transition: transform 0.35s cubic-bezier(0.16, 1, 0.3, 1), opacity 0.3s ease;
  opacity: 0;
}

.edtech-toast.show {
  transform: translateX(0);
  opacity: 1;
}

.edtech-toast-icon {
  font-size: 1.25rem;
  flex-shrink: 0;
}

.edtech-toast.success {
  border-left: 4px solid var(--secondary);
}

.edtech-toast.warning {
  border-left: 4px solid var(--accent-amber);
}

.edtech-toast.error {
  border-left: 4px solid var(--accent-red);
}

/* ================= MOBILE BOTTOM NAVIGATION DOCK 2.0 (APP-LIKE FEEL) ================= */
.mobile-bottom-nav {
  display: none;
}

@media (max-width: 768px) {
  body:not(.in-classroom) {
    padding-bottom: calc(76px + env(safe-area-inset-bottom, 0px)) !important; /* Đảm bảo không bị che nội dung đáy */
  }

  .mobile-bottom-nav {
    display: flex;
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    height: calc(62px + env(safe-area-inset-bottom, 0px));
    background: rgba(255, 255, 255, 0.90);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-top: 1px solid rgba(226, 232, 240, 0.85);
    z-index: 1000;
    align-items: center;
    justify-content: space-around;
    padding: 0 8px env(safe-area-inset-bottom, 0px);
    box-shadow: 0 -4px 20px rgba(15, 23, 42, 0.08);
  }

  .mobile-bottom-nav-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 3px;
    color: var(--muted);
    font-size: 0.72rem;
    font-weight: 600;
    text-decoration: none;
    flex: 1;
    height: 100%;
    min-height: 48px;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    touch-action: manipulation;
    -webkit-tap-highlight-color: transparent;
    user-select: none;
    -webkit-user-select: none;
    position: relative;
    border-radius: 12px;
  }

  .mobile-bottom-nav-item .nav-icon {
    font-size: 1.25rem;
    line-height: 1;
    transition: transform 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  }

  .mobile-bottom-nav-item:hover,
  .mobile-bottom-nav-item.active {
    color: var(--primary);
  }

  .mobile-bottom-nav-item.active {
    font-weight: 700;
  }

  .mobile-bottom-nav-item.active .nav-icon {
    transform: translateY(-2px) scale(1.15);
  }

  .mobile-bottom-nav-item:active {
    transform: scale(0.92);
  }
}

/* ================= STICKY MOBILE CHECKOUT BAR ================= */
.mobile-sticky-checkout {
  display: none;
}

@media (max-width: 850px) {
  .mobile-sticky-checkout {
    display: flex;
    align-items: center;
    justify-content: space-between;
    position: fixed;
    bottom: calc(64px + env(safe-area-inset-bottom, 0px));
    left: 0;
    right: 0;
    background: var(--bg-frosted);
    backdrop-filter: blur(14px);
    -webkit-backdrop-filter: blur(14px);
    border-top: 1px solid var(--border);
    padding: 10px 18px;
    z-index: 999;
    box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.08);
  }

  .mobile-sticky-checkout .price-info {
    display: flex;
    flex-direction: column;
  }

  .mobile-sticky-checkout .price-current {
    font-size: 1.3rem;
    font-weight: 800;
    color: var(--accent-red);
    line-height: 1.1;
  }

  .mobile-sticky-checkout .price-original {
    font-size: 0.8rem;
    color: var(--muted);
    text-decoration: line-through;
  }

  .mobile-sticky-checkout .btn-buy-mobile {
    background: var(--primary-gradient);
    color: var(--text-on-primary);
    font-weight: 700;
    padding: 10px 22px;
    border-radius: var(--radius-sm);
    font-size: 0.92rem;
    border: none;
    cursor: pointer;
    box-shadow: 0 4px 14px rgba(37, 99, 235, 0.35);
  }
}

/* ================= FINTECH PAYMENT RADAR ================= */
.radar-box {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 16px auto;
  width: 250px;
  max-width: 100%;
}

.radar-scanner {
  position: absolute;
  inset: -8px;
  border-radius: 16px;
  pointer-events: none;
  overflow: hidden;
}

.radar-wave {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 5px;
  background: linear-gradient(180deg, rgba(6, 182, 212, 0) 0%, rgba(6, 182, 212, 0.8) 50%, rgba(37, 99, 235, 1) 100%);
  box-shadow: 0 0 16px 4px rgba(6, 182, 212, 0.6);
  animation: scanWave 2.8s ease-in-out infinite alternate;
}

@keyframes scanWave {
  0% { transform: translateY(0); opacity: 0.4; }
  50% { opacity: 1; }
  100% { transform: translateY(240px); opacity: 0.4; }
}

.pulse-circle {
  position: absolute;
  width: 100%;
  height: 100%;
  border-radius: 14px;
  border: 1.5px solid rgba(37, 99, 235, 0.35);
  animation: pulseOut 2.4s cubic-bezier(0.16, 1, 0.3, 1) infinite;
  pointer-events: none;
}

@keyframes pulseOut {
  0% { transform: scale(0.97); opacity: 0.8; }
  100% { transform: scale(1.05); opacity: 0; }
}

/* ================= COURSE DETAILS TABS & ACCORDION ================= */
.course-tabs-nav {
  display: flex;
  gap: 8px;
  border-bottom: 2px solid var(--border);
  margin-bottom: 24px;
  overflow-x: auto;
  scrollbar-width: none;
}
.course-tabs-nav::-webkit-scrollbar { display: none; }

.course-tab-item {
  padding: 12px 18px;
  font-weight: 700;
  font-size: 0.95rem;
  color: var(--muted);
  background: transparent;
  border: none;
  border-bottom: 3px solid transparent;
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.2s;
  margin-bottom: -2px;
}

.course-tab-item:hover, .course-tab-item.active {
  color: var(--primary);
  border-bottom-color: var(--primary);
}

.faq-card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 12px;
  overflow: hidden;
  transition: all 0.2s;
}

.faq-card:hover {
  border-color: var(--border);
}

.faq-question {
  padding: 16px 20px;
  font-weight: 700;
  color: var(--dark);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
}

.faq-answer {
  padding: 0 20px 16px;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.6;
}

/* ================= LEARNER ACADEMY DASHBOARD ================= */
.learner-banner {
  background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 50%, #4338ca 100%);
  color: var(--text-on-primary);
  border-radius: var(--radius-lg);
  padding: 32px;
  margin-bottom: 30px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 20px;
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
}

.learner-banner::after {
  content: "";
  position: absolute;
  right: -50px;
  top: -50px;
  width: 200px;
  height: 200px;
  background: radial-gradient(circle, rgba(255,255,255,0.15) 0%, rgba(255,255,255,0) 70%);
  border-radius: 50%;
}

.streak-fire-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(245, 158, 11, 0.25);
  border: 1px solid rgba(245, 158, 11, 0.5);
  color: #fef08a;
  padding: 6px 14px;
  border-radius: var(--radius-full);
  font-weight: 800;
  font-size: 0.88rem;
}

.progress-bar-wrap {
  width: 100%;
  height: 7px;
  background: var(--bg-surface-soft);
  border-radius: 10px;
  overflow: hidden;
  margin: 10px 0;
}

.progress-bar-fill {
  height: 100%;
  background: linear-gradient(90deg, #2563eb 0%, #10b981 100%);
  border-radius: 10px;
  transition: width 0.6s ease;
}

/* ================= CINEMA CLASSROOM LECTURE CONTROLS ================= */
.lecture-controls-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 20px;
  background: var(--cinema-surface);
  border-top: 1px solid var(--cinema-border);
  color: var(--text-muted);
  font-size: 0.85rem;
  gap: 12px;
  flex-wrap: wrap;
}

.controls-nav-group {
  display: flex;
  align-items: center;
  gap: 10px;
}

.btn-lecture-nav {
  min-height: 38px;
  padding: 6px 14px;
  font-size: 0.85rem;
  border-radius: 8px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  white-space: nowrap;
  font-weight: 600;
  transition: all 0.2s ease;
}

.controls-utility-group {
  display: flex;
  align-items: center;
  gap: 16px;
}

.speed-controls-box {
  display: flex;
  align-items: center;
  gap: 8px;
}

.speed-label {
  font-size: 0.78rem;
  color: var(--text-muted);
  white-space: nowrap;
  font-weight: 600;
}

.speed-pill-group {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  background: rgba(255, 255, 255, 0.05);
  padding: 3px 4px;
  border-radius: 8px;
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.speed-selector-pill {
  background: transparent;
  border: none;
  color: #cbd5e1;
  padding: 4px 8px;
  border-radius: 6px;
  font-size: 0.78rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s ease;
  min-height: 28px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.speed-selector-pill:hover {
  background: rgba(255, 255, 255, 0.12);
  color: #ffffff;
}

.speed-selector-pill.active {
  background: var(--primary);
  color: #ffffff;
  box-shadow: 0 2px 6px rgba(37, 99, 235, 0.4);
}

.btn-quiz-jump {
  padding: 6px 14px;
  font-size: 0.85rem;
  border-color: #38bdf8;
  color: #38bdf8;
  background: rgba(56, 189, 248, 0.1);
  min-height: 38px;
  border-radius: 8px;
  white-space: nowrap;
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: all 0.2s ease;
}

.btn-quiz-jump:hover {
  background: rgba(56, 189, 248, 0.2);
  transform: translateY(-1px);
}

/* ================= LESSON INTERACTIVE MINI GAME QUIZ ================= */
.lesson-quiz-section {
  padding: 36px 20px 64px;
  background: linear-gradient(180deg, #090d16 0%, #0f172a 100%);
  border-top: 2px solid rgba(56, 189, 248, 0.2);
  color: #f8fafc;
}

.lesson-quiz-card {
  max-width: 780px;
  margin: 0 auto;
  background: rgba(15, 23, 42, 0.94);
  border: 1.5px solid rgba(56, 189, 248, 0.25);
  border-radius: 20px;
  padding: 28px 24px;
  box-shadow: 0 20px 45px -15px rgba(0, 0, 0, 0.7), 0 0 35px rgba(14, 165, 233, 0.12);
  backdrop-filter: blur(14px);
  position: relative;
}

.quiz-header-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
  flex-wrap: wrap;
  gap: 12px;
}

.quiz-badge-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(56, 189, 248, 0.15);
  border: 1px solid rgba(56, 189, 248, 0.4);
  color: #38bdf8;
  font-weight: 800;
  font-size: 0.85rem;
  padding: 6px 14px;
  border-radius: 30px;
  letter-spacing: 0.5px;
}

.quiz-stats-hud {
  display: flex;
  align-items: center;
  gap: 10px;
}

.quiz-score-pill {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.92rem;
  font-weight: 700;
  color: #f8fafc;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.15);
  padding: 4px 12px;
  border-radius: 8px;
}

.quiz-question-box {
  background: rgba(30, 41, 59, 0.8);
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 14px;
  padding: 20px 22px;
  font-size: 1.1rem;
  font-weight: 700;
  color: #ffffff;
  line-height: 1.6;
  margin-bottom: 20px;
  box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.3);
}

.quiz-options-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

@media (max-width: 640px) {
  .quiz-options-grid {
    grid-template-columns: 1fr;
  }
}

.quiz-opt-btn {
  background: rgba(30, 41, 59, 0.85);
  border: 1.5px solid rgba(148, 163, 184, 0.2);
  color: #e2e8f0;
  padding: 14px 18px;
  border-radius: 12px;
  font-size: 0.96rem;
  font-weight: 600;
  text-align: left;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex;
  align-items: center;
  gap: 12px;
  position: relative;
  min-height: 52px;
}

.quiz-opt-btn:hover:not(:disabled) {
  background: rgba(56, 189, 248, 0.15);
  border-color: #38bdf8;
  color: #ffffff;
  transform: translateY(-2px);
  box-shadow: 0 4px 14px rgba(56, 189, 248, 0.25);
}

.quiz-opt-btn.correct-flash {
  background: linear-gradient(135deg, #059669 0%, #10b981 100%) !important;
  border-color: #34d399 !important;
  color: #ffffff !important;
  box-shadow: 0 0 25px rgba(16, 185, 129, 0.5) !important;
  animation: quizSuccessPulse 0.5s ease-out;
}

.quiz-opt-btn.wrong-flash {
  background: linear-gradient(135deg, #dc2626 0%, #ef4444 100%) !important;
  border-color: #f87171 !important;
  color: #ffffff !important;
  box-shadow: 0 0 25px rgba(239, 68, 68, 0.5) !important;
  animation: quizShake 0.4s ease-in-out;
}

@keyframes quizSuccessPulse {
  0% { transform: scale(0.97); }
  50% { transform: scale(1.03); }
  100% { transform: scale(1); }
}

@keyframes quizShake {
  0%, 100% { transform: translateX(0); }
  20%, 60% { transform: translateX(-6px); }
  40%, 80% { transform: translateX(6px); }
}

.quiz-feedback-box {
  margin-top: 18px;
  padding: 14px 18px;
  border-radius: 10px;
  font-size: 0.95rem;
  font-weight: 600;
  display: none;
  animation: fadeIn 0.3s ease;
}

.quiz-feedback-box.show {
  display: block;
}

.quiz-feedback-box.correct {
  background: rgba(16, 185, 129, 0.15);
  border: 1px solid rgba(52, 211, 153, 0.4);
  color: #34d399;
}

.quiz-feedback-box.wrong {
  background: rgba(239, 68, 68, 0.15);
  border: 1px solid rgba(248, 113, 113, 0.4);
  color: #f87171;
}

.quiz-footer-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 20px;
  padding-top: 16px;
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  flex-wrap: wrap;
  gap: 12px;
}

/* ================= HEADER AUTH DESKTOP WRAP FIX ================= */
.header-auth-desktop {
  display: flex;
  align-items: center;
  white-space: nowrap;
  flex-shrink: 0;
}

/* ================= GLOBAL DARK THEME & RESPONSIVE POLISH ================= */
.footer {
  background: var(--bg-surface);
  border-top: 1px solid var(--border-color);
  padding: 48px 0 32px;
  margin-top: 60px;
  text-align: center;
  color: var(--text-secondary);
  transition: background-color 0.25s ease, border-color 0.25s ease;
}

[data-theme="dark"] .stats-bar {
  background: rgba(17, 24, 39, 0.94);
  border-color: rgba(30, 41, 59, 0.9);
}

[data-theme="dark"] .stat-num {
  color: #f8fafc;
}

[data-theme="dark"] .stat-icon {
  background: rgba(59, 130, 246, 0.15);
  border-color: rgba(59, 130, 246, 0.3);
}

[data-theme="dark"] .shelf-section {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

[data-theme="dark"] .shelf-section.shelf-accent-12 {
  background: linear-gradient(180deg, rgba(220, 38, 38, 0.08) 0%, var(--bg-surface) 120px);
}

[data-theme="dark"] .shelf-section.shelf-accent-11 {
  background: linear-gradient(180deg, rgba(37, 99, 235, 0.08) 0%, var(--bg-surface) 120px);
}

[data-theme="dark"] .shelf-section.shelf-accent-10 {
  background: linear-gradient(180deg, rgba(5, 150, 105, 0.08) 0%, var(--bg-surface) 120px);
}

[data-theme="dark"] .chapter-card-box {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

[data-theme="dark"] .chapter-card-header {
  border-bottom-color: var(--border-color);
}

[data-theme="dark"] .chapter-badge-branch {
  background: var(--bg-surface-soft);
  color: var(--text-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .chapter-tip-box {
  background: rgba(245, 158, 11, 0.12);
  border-color: rgba(245, 158, 11, 0.25);
  color: #fde68a;
}

[data-theme="dark"] .mobile-drawer {
  background: var(--bg-surface);
  color: var(--text-main);
}

[data-theme="dark"] .mobile-drawer-header {
  border-bottom-color: var(--border-color);
}

[data-theme="dark"] .mobile-nav-link {
  color: var(--text-secondary);
}

[data-theme="dark"] .mobile-nav-link:hover,
[data-theme="dark"] .mobile-nav-link.active {
  background: var(--primary-light);
  color: var(--primary);
}

[data-theme="dark"] .mobile-bottom-nav {
  background: rgba(15, 23, 42, 0.88);
  border-top-color: rgba(30, 41, 59, 0.8);
  box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .mobile-bottom-nav-item {
  color: var(--text-muted);
}

[data-theme="dark"] .mobile-bottom-nav-item.active {
  color: #38bdf8;
}

/* ================= DARK MODE POLISH CHO K12 KHÁM PHÁ KHÓA HỌC ================= */
[data-theme="dark"] .k12-chapter-lesson-item {
  background: rgba(30, 41, 59, 0.65);
  border-color: rgba(51, 65, 85, 0.75);
}

[data-theme="dark"] .k12-chapter-lesson-item:hover {
  background: rgba(30, 41, 59, 0.95);
  border-color: var(--primary);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .k12-chapter-lesson-item .lesson-chip-num {
  background: rgba(59, 130, 246, 0.2);
  color: #60a5fa;
  border-color: rgba(59, 130, 246, 0.35);
}

[data-theme="dark"] .k12-chapter-lesson-item .lesson-chip-name {
  color: #f8fafc;
}

[data-theme="dark"] .k12-chapter-lesson-item:hover .lesson-chip-name {
  color: #60a5fa;
}

[data-theme="dark"] .k12-chapter-lesson-item:hover .lesson-chip-arrow {
  color: #60a5fa;
}

[data-theme="dark"] .k12-sidebar-lesson-item.active {
  background: rgba(59, 130, 246, 0.2);
  color: #60a5fa;
}

[data-theme="dark"] .k12-search-input {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .k12-search-input:focus {
  border-color: var(--primary);
  background: var(--bg-surface);
}

[data-theme="dark"] .badge-3d-pill {
  background: rgba(16, 185, 129, 0.18);
  color: #34d399;
  border-color: rgba(52, 211, 153, 0.35);
}

[data-theme="dark"] .badge-demo-pill {
  background: rgba(239, 68, 68, 0.18);
  color: #f87171;
}

[data-theme="dark"] .shelf-badge.blue {
  background: rgba(59, 130, 246, 0.18);
  color: #93c5fd;
  border: 1px solid rgba(59, 130, 246, 0.35);
}

[data-theme="dark"] .shelf-badge.green {
  background: rgba(16, 185, 129, 0.18);
  color: #6ee7b7;
  border: 1px solid rgba(16, 185, 129, 0.35);
}

[data-theme="dark"] .shelf-badge.orange {
  background: rgba(245, 158, 11, 0.18);
  color: #fde68a;
  border: 1px solid rgba(245, 158, 11, 0.35);
}

[data-theme="dark"] .shelf-badge.red {
  background: rgba(239, 68, 68, 0.18);
  color: #fca5a5;
  border: 1px solid rgba(239, 68, 68, 0.35);
}

/* ================= COMPREHENSIVE DARK MODE OVERRIDES (FULL POLISH) ================= */

/* Specificity fix for Stats Bar */
[data-theme="dark"] .stat-item .stat-num {
  color: #f8fafc !important;
}

/* Hero Section in Dark Mode */
[data-theme="dark"] .hero {
  background: 
    radial-gradient(ellipse 80% 50% at 50% -15%, rgba(37, 99, 235, 0.25), transparent 70%),
    radial-gradient(circle at 92% 35%, rgba(6, 182, 212, 0.15), transparent 45%),
    radial-gradient(circle at 8% 75%, rgba(16, 185, 129, 0.1), transparent 45%),
    var(--bg-page);
  border-bottom-color: var(--border-color);
}

[data-theme="dark"] .hero-content-full .hero-title {
  color: var(--text-main);
}

[data-theme="dark"] .hero-content-full .hero-subtitle {
  color: var(--text-secondary);
}

[data-theme="dark"] .guarantee-pill-item {
  background: rgba(30, 41, 59, 0.85);
  border-color: rgba(51, 65, 85, 0.9);
  color: var(--text-main);
  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.3);
}

[data-theme="dark"] .guarantee-pill-item:hover {
  border-color: var(--primary);
  background: rgba(30, 41, 59, 0.98);
}

[data-theme="dark"] .btn-outline-trial {
  background: rgba(30, 41, 59, 0.85);
  border-color: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .btn-outline-trial:hover {
  background: var(--primary-light);
  border-color: var(--primary);
  color: var(--primary);
}

[data-theme="dark"] .math-sandbox-card {
  background: rgba(17, 24, 39, 0.92);
  border-color: var(--border-color);
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5), 0 0 0 1px rgba(255, 255, 255, 0.08) inset;
}

[data-theme="dark"] .sandbox-tabs {
  background: var(--bg-surface-soft);
}

[data-theme="dark"] .sandbox-tab-btn {
  color: var(--text-muted);
}

[data-theme="dark"] .sandbox-tab-btn:hover {
  color: var(--text-main);
}

[data-theme="dark"] .sandbox-tab-btn.active {
  background: var(--bg-surface-elevated);
  color: #60a5fa;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.4);
}

/* Testimonials in Dark Mode (Fixes Contrast bug 1.06:1) */
[data-theme="dark"] .testimonial-card {
  background: var(--bg-surface);
  border-color: var(--border-color);
  box-shadow: var(--shadow);
}

[data-theme="dark"] .testimonial-quote {
  color: var(--text-secondary);
}

[data-theme="dark"] .author-info h4 {
  color: var(--text-main);
}

[data-theme="dark"] .author-info p {
  color: var(--text-muted);
}

[data-theme="dark"] .score-badge {
  background: rgba(16, 185, 129, 0.15);
  color: #34d399;
  border: 1px solid rgba(52, 211, 153, 0.3);
}

/* FAQ Accordion in Dark Mode (Fixes Contrast bug 1.06:1) */
[data-theme="dark"] .faq-card {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

[data-theme="dark"] .faq-question {
  color: var(--text-main);
}

[data-theme="dark"] .faq-answer {
  color: var(--text-secondary);
}

/* Chapter & Lesson Cards in Dark Mode */
[data-theme="dark"] .chapter-lesson-card {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
}

[data-theme="dark"] .chapter-lesson-card:hover {
  background: var(--bg-surface-elevated);
  border-color: var(--primary);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .lesson-title {
  color: var(--text-main);
}

[data-theme="dark"] .lesson-hook {
  color: var(--text-secondary);
}

[data-theme="dark"] .badge-chip {
  background: var(--bg-surface);
  border-color: var(--border-color);
  color: var(--text-secondary);
}

/* Dạng bài học rows */
[data-theme="dark"] .dang-item-row {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

[data-theme="dark"] .dang-item-row:hover {
  background: var(--bg-surface-elevated);
}

[data-theme="dark"] .dang-title {
  color: var(--text-main);
}

[data-theme="dark"] .dang-desc {
  color: var(--text-secondary);
}

[data-theme="dark"] .btn-learn-dang {
  background: transparent;
  color: #60a5fa !important;
  border-color: var(--primary);
}

[data-theme="dark"] .btn-learn-dang:hover {
  background: var(--primary-light);
  color: #93c5fd !important;
}

/* Chapter Lesson Sequential Row */
[data-theme="dark"] .chapter-lesson-row {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
}

[data-theme="dark"] .chapter-lesson-row:hover {
  background: var(--bg-surface-elevated);
  border-color: var(--primary);
}

[data-theme="dark"] .lesson-row-title {
  color: var(--text-main);
}

[data-theme="dark"] .lesson-row-hook {
  color: var(--text-secondary);
}

/* Shelf Section Accent THCS */
[data-theme="dark"] .shelf-section.shelf-accent-thcs {
  background: linear-gradient(180deg, rgba(234, 88, 12, 0.08) 0%, var(--bg-surface) 120px);
}

/* Multi-language Popover in Dark Mode */
[data-theme="dark"] .lang-menu-popover {
  background: var(--bg-surface-elevated);
  border-color: var(--border-color);
  box-shadow: 0 14px 35px -5px rgba(0, 0, 0, 0.6), 0 8px 16px -6px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .lang-menu-header {
  border-bottom-color: var(--border-color);
  color: var(--text-muted);
}

[data-theme="dark"] .lang-menu-close {
  color: var(--text-muted);
}

[data-theme="dark"] .lang-menu-close:hover {
  background: var(--bg-surface-soft);
  color: var(--text-main);
}

[data-theme="dark"] .lang-search-input {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .lang-search-input:focus {
  background: var(--bg-surface);
  border-color: var(--primary);
}

[data-theme="dark"] .lang-menu-item.core-item {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
}

[data-theme="dark"] .lang-menu-item.core-item:hover {
  background: var(--bg-surface);
  border-color: var(--primary);
}

[data-theme="dark"] .lang-menu-item.core-item.active {
  background: var(--primary-light);
  border-color: var(--primary);
}

[data-theme="dark"] .lang-menu-item .name {
  color: var(--text-main);
}

[data-theme="dark"] .lang-menu-item .desc {
  color: var(--text-muted);
}

[data-theme="dark"] .lang-other-btn {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
  color: var(--text-secondary);
}

[data-theme="dark"] .lang-other-btn:hover {
  background: var(--bg-surface);
  border-color: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .lang-other-btn.active {
  background: var(--primary-light);
  border-color: var(--primary);
  color: #60a5fa;
}

[data-theme="dark"] .lang-menu-footer {
  border-top-color: var(--border-color);
  color: var(--text-muted);
}

/* Mobile Drawer Elements in Dark Mode */
[data-theme="dark"] .mobile-drawer-close {
  background: var(--bg-surface-soft);
  color: var(--text-muted);
}

[data-theme="dark"] .mobile-drawer-close:hover {
  background: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .mobile-drawer-footer {
  background: var(--bg-surface-soft);
  border-top-color: var(--border-color);
}

/* Mobile Sticky Checkout in Dark Mode */
[data-theme="dark"] .mobile-sticky-checkout {
  background: rgba(17, 24, 39, 0.96);
  border-top-color: var(--border-color);
  box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.5);
}

/* Grade Filter Pills in Dark Mode */
[data-theme="dark"] .grade-pill-btn {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
  color: var(--text-secondary);
}

[data-theme="dark"] .grade-pill-btn:hover {
  background: var(--border-color);
  color: var(--text-main);
}

[data-theme="dark"] .grade-pill-btn.active {
  background: var(--primary);
  border-color: var(--primary);
  color: #ffffff;
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.4);
}

[data-theme="dark"] .sidebar-grade-btn {
  color: var(--text-secondary);
}

[data-theme="dark"] .sidebar-grade-btn:hover {
  background: var(--bg-surface-soft);
  color: var(--text-main);
}

[data-theme="dark"] .sidebar-grade-btn.active {
  background: var(--primary);
  color: #ffffff;
}

/* Price current contrast enhancement in Dark Mode */
[data-theme="dark"] .price-current {
  color: #f87171;
}

/* Copy button hover fix in Dark Mode */
[data-theme="dark"] .btn-copy {
  background: var(--primary-light);
  border-color: rgba(59, 130, 246, 0.3);
  color: #60a5fa;
}

[data-theme="dark"] .btn-copy:hover {
  background: rgba(59, 130, 246, 0.25);
  color: #93c5fd;
}

/* User profile card & avatar in Dark Mode */
[data-theme="dark"] .user-profile {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

[data-theme="dark"] .avatar-stack img {
  border-color: var(--bg-surface);
}

/* Level tabs in Dark Mode */
[data-theme="dark"] .level-tab-btn {
  background: var(--bg-surface);
  border-color: var(--border-color);
  color: var(--text-secondary);
}

[data-theme="dark"] .level-tab-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
}

[data-theme="dark"] .level-tab-btn.active {
  background: var(--primary-gradient);
  border-color: transparent;
  color: #ffffff;
}

/* Course Detail Page Components in Dark Mode */
[data-theme="dark"] .purchase-card {
  background: var(--bg-surface);
  border-color: var(--border-color);
  box-shadow: var(--shadow-md);
}

[data-theme="dark"] .instructor-card {
  background: var(--bg-surface-soft);
  border-color: var(--border-color);
}

[data-theme="dark"] .benefit-item {
  background: var(--bg-surface);
  border-color: var(--border-color);
}

/* Classroom / Cinema Mode adaptive styling (User approved theme change) */
[data-theme="light"] body.in-classroom {
  background: #f1f5f9 !important;
}

[data-theme="light"] .classroom-topbar {
  background: #ffffff;
  border-bottom-color: #e2e8f0;
  color: #0f172a;
}

[data-theme="light"] .classroom-topbar #topLessonTitle {
  color: #0f172a !important;
}

[data-theme="light"] .classroom-topbar #topCourseTitle {
  color: #64748b !important;
}

[data-theme="light"] .btn-cinema-action {
  background: rgba(0, 0, 0, 0.05);
  border-color: #cbd5e1;
  color: #1e293b;
}

[data-theme="light"] .btn-cinema-action:hover {
  background: rgba(0, 0, 0, 0.08);
}

[data-theme="light"] .syllabus-sidebar {
  background: #ffffff;
  border-left-color: #e2e8f0;
  color: #0f172a;
}

[data-theme="light"] .syllabus-header {
  border-bottom-color: #e2e8f0;
}

[data-theme="light"] .syllabus-item {
  background: #f8fafc;
  color: #334155;
  border-color: #e2e8f0;
}

[data-theme="light"] .syllabus-item:hover {
  background: #eff6ff;
  color: #1d4ed8;
}

[data-theme="light"] .syllabus-item.active {
  background: #eff6ff;
  border-color: var(--primary);
  color: var(--primary);
}

[data-theme="light"] .syllabus-number {
  background: #e2e8f0;
  color: #1e293b;
}

[data-theme="light"] .syllabus-item.active .syllabus-number {
  background: var(--primary);
  color: #ffffff;
}

[data-theme="light"] .viewer-area {
  background: #e2e8f0;
}

[data-theme="light"] #sidebarCourseTitle,
[data-theme="light"] .syllabus-header h3 {
  color: #0f172a !important;
}

[data-theme="light"] .syllabus-header div,
[data-theme="light"] #progressText {
  color: #64748b !important;
}