/* ==========================================================================
   FSRS-6 Flashcard Pro - Design Tokens, Variables & Reset
   ========================================================================== */

:root,
[data-theme="dark"] {
  /* Color Palette - Dark Theme Default (Zen Charcoal #18181B / Deep Carbon) */
  --bg-primary: #18181b;
  --bg-secondary: #202024;
  --bg-tertiary: #27272a;
  --bg-card: #202024;
  --bg-glass: rgba(24, 24, 27, 0.92);
  
  --text-primary: #fafafa;
  --text-secondary: #a1a1aa;
  --text-muted: #71717a;
  
  --primary: #4f46e5;
  --primary-glow: rgba(79, 70, 229, 0.18);
  --primary-light: #6366f1;
  
  --accent: #0284c7;
  
  /* FSRS Ratings Colors - Clean Outline Accents */
  --fsrs-again: #ef4444;
  --fsrs-again-bg: rgba(239, 68, 68, 0.06);
  --fsrs-hard: #f59e0b;
  --fsrs-hard-bg: rgba(245, 158, 11, 0.06);
  --fsrs-good: #10b981;
  --fsrs-good-bg: rgba(16, 185, 129, 0.06);
  --fsrs-easy: #3b82f6;
  --fsrs-easy-bg: rgba(59, 130, 246, 0.06);

  --border: rgba(255, 255, 255, 0.08);
  --border-focus: rgba(99, 102, 241, 0.4);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-xl: 18px;
  --radius-2xl: 24px;
  --radius-full: 9999px;

  --transition-fast: 0.12s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-smooth: 0.3s cubic-bezier(0.16, 1, 0.3, 1);

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.12);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.18);
  --shadow-lg: 0 12px 28px rgba(0, 0, 0, 0.24);

  --nav-height: 60px;
  --safe-bottom: env(safe-area-inset-bottom, 12px);
  --font-main: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
}

[data-theme="light"] {
  /* Warm off-white paper canvas (#FAFAFA / Notion / Linear style) */
  --bg-primary: #fafafa;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f4f4f5;
  --bg-card: #ffffff;
  --bg-glass: rgba(250, 250, 250, 0.94);

  --text-primary: #18181b;
  --text-secondary: #71717a;
  --text-muted: #a1a1aa;

  --border: #e5e7eb;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.03);
  --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.06);

  --primary: #4f46e5;
  --primary-light: #6366f1;

  --fsrs-again: #e11d48;
  --fsrs-again-bg: rgba(225, 29, 72, 0.05);
  --fsrs-hard: #d97706;
  --fsrs-hard-bg: rgba(217, 119, 6, 0.05);
  --fsrs-good: #059669;
  --fsrs-good-bg: rgba(5, 150, 105, 0.05);
  --fsrs-easy: #2563eb;
  --fsrs-easy-bg: rgba(37, 99, 235, 0.05);
}

/* Base Reset & Chống bôi đen văn bản toàn bộ ứng dụng */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  -webkit-tap-highlight-color: transparent;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}

/* Cho phép nhập liệu và chọn văn bản trong ô input, textarea */
input, textarea {
  -webkit-user-select: auto;
  -moz-user-select: auto;
  -ms-user-select: auto;
  user-select: auto;
}

html, body {
  width: 100%;
  height: 100%;
  height: 100dvh;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 15px;
  line-height: 1.5;
  overflow: hidden;
  -webkit-touch-callout: none;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

/* ==========================================================================
   Global Floating Scrollbar Styling (iOS / macOS Ultra-Sleek Pill)
   ========================================================================== */
* {
  scrollbar-width: thin;
  scrollbar-color: rgba(99, 102, 241, 0.28) transparent;
}

::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: rgba(99, 102, 241, 0.25);
  border-radius: 9999px;
  border: 1px solid transparent;
  background-clip: padding-box;
  transition: background-color 0.2s ease;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(99, 102, 241, 0.55);
  background-clip: padding-box;
}

::-webkit-scrollbar-corner {
  background: transparent;
}

[data-theme="light"] * {
  scrollbar-color: rgba(99, 102, 241, 0.3) transparent;
}

[data-theme="light"] ::-webkit-scrollbar-thumb {
  background: rgba(99, 102, 241, 0.28);
}

[data-theme="light"] ::-webkit-scrollbar-thumb:hover {
  background: rgba(99, 102, 241, 0.58);
}

/* ==========================================================================
   FSRS-6 Flashcard Pro - Layout & Navigation (Mobile-First + Desktop PC Sidebar)
   ========================================================================== */

/* App Container Frame - Mobile Default (True 100dvh App Shell) */
#app-container {
  width: 100%;
  max-width: 480px;
  height: 100vh;
  height: 100dvh;
  max-height: 100vh;
  max-height: 100dvh;
  margin: 0 auto;
  position: relative;
  background-color: var(--bg-primary);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  box-shadow: 0 0 50px rgba(0, 0, 0, 0.5);
}

/* Top App Header (Mobile) - Fixed in Flex flow */
.app-header {
  order: 1;
  flex-shrink: 0;
  position: relative;
  top: 0;
  z-index: 40;
  padding: 14px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.brand-wrapper {
  display: flex;
  align-items: center;
  gap: 10px;
}

.brand-icon {
  width: 34px;
  height: 34px;
  background: linear-gradient(135deg, #6366f1, #4f46e5);
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  color: #ffffff;
  flex-shrink: 0;
  box-shadow: 0 2px 8px rgba(99, 102, 241, 0.3);
}

.brand-info {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 1px;
}

.brand-title {
  font-size: 0.98rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  line-height: 1.2;
  white-space: nowrap;
}

.brand-sub {
  font-size: 0.65rem;
  font-weight: 700;
  color: var(--primary);
  background: rgba(99, 102, 241, 0.12);
  padding: 1px 6px;
  border-radius: 4px;
  letter-spacing: 0.04em;
  display: inline-block;
  line-height: 1.2;
}

[data-theme="light"] .brand-sub {
  color: #4f46e5;
  background: #eef2ff;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 6px;
}

.header-actions .btn-icon {
  width: 34px;
  height: 34px;
  border-radius: 9px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: 0.92rem;
  transition: all 0.18s ease;
  touch-action: manipulation;
  padding: 0;
  outline: none;
  flex-shrink: 0;
}

.header-actions .btn-icon:hover {
  background: rgba(99, 102, 241, 0.12);
  border-color: rgba(99, 102, 241, 0.3);
  color: var(--primary);
}

.header-actions .btn-icon:active {
  transform: scale(0.94);
}

.header-actions .btn-header-profile svg,
.header-actions .btn-header-settings svg {
  width: 18px;
  height: 18px;
}

.header-actions .btn-header-profile.active,
.header-actions .btn-header-settings.active {
  background: var(--primary);
  color: #ffffff;
  border-color: var(--primary);
}

.streak-pill {
  display: flex;
  align-items: center;
  gap: 4px;
  background: rgba(245, 158, 11, 0.1);
  border: 1px solid rgba(245, 158, 11, 0.25);
  color: #f59e0b;
  padding: 3px 9px;
  border-radius: var(--radius-full);
  font-weight: 700;
  font-size: 0.78rem;
  white-space: nowrap;
  flex-shrink: 0;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  user-select: none;
}

.streak-pill:hover {
  background: rgba(245, 158, 11, 0.18);
  border-color: rgba(245, 158, 11, 0.45);
  transform: translateY(-1px);
}

.streak-pill.streak-broken-alert {
  background: rgba(239, 68, 68, 0.14);
  border-color: rgba(239, 68, 68, 0.4);
  color: #ef4444;
  animation: pulseBrokenStreak 2s infinite ease-in-out;
}

@keyframes pulseBrokenStreak {
  0%, 100% {
    box-shadow: 0 0 0 0 rgba(239, 68, 68, 0.45);
    transform: scale(1);
  }
  50% {
    box-shadow: 0 0 0 5px rgba(239, 68, 68, 0);
    transform: scale(1.03);
  }
}

[data-theme="dark"] .streak-pill {
  color: #fbbf24;
}

[data-theme="dark"] .streak-pill.streak-broken-alert {
  color: #f87171;
}

/* Main Tab View Area - The ONLY scrollable region */
.tab-content-area {
  order: 2;
  flex: 1;
  min-height: 0;
  height: auto;
  display: flex;
  flex-direction: column;
  overflow-y: auto;
  overflow-x: hidden;
  -webkit-overflow-scrolling: touch;
  padding-bottom: 0;
  position: relative;
}

/* Tinh chỉnh thanh cuộn cho mượt mà */
.tab-content-area::-webkit-scrollbar {
  width: 4px;
}
.tab-content-area::-webkit-scrollbar-track {
  background: transparent;
}
.tab-content-area::-webkit-scrollbar-thumb {
  background: rgba(99, 102, 241, 0.2);
  border-radius: var(--radius-full);
}
.tab-content-area::-webkit-scrollbar-thumb:hover {
  background: rgba(99, 102, 241, 0.4);
}

.tab-pane {
  display: none;
  padding: 16px 16px 24px 16px;
  animation: fadeIn 0.25s ease-out;
}

.tab-pane.active {
  display: block;
}

#tab-review.tab-pane.active {
  display: flex;
  flex-direction: column;
  flex: 1;
  min-height: 0;
  padding: 12px 16px;
}

@media (max-width: 480px) {
  .app-header {
    padding: 10px 14px;
  }
  .tab-pane {
    padding: 12px 10px 14px 10px;
  }
}

/* ==========================================================================
   📱 iOS Inset Grouped Design System (Shared Components)
   ========================================================================== */
.section-group,
.settings-group,
.profile-group,
.stats-section-group,
.bento-section-group {
  display: flex;
  flex-direction: column;
  margin-bottom: 16px;
  width: 100%;
}

.section-group-header {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 3px;
  padding: 0 4px;
  margin-bottom: 7px;
  text-align: left;
  width: 100%;
}

.section-group-title {
  font-size: 0.82rem;
  font-weight: 800;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  text-align: left;
  gap: 6px;
  margin: 0;
}

[data-theme="light"] .section-group-title {
  color: #1e293b;
}

[data-theme="dark"] .section-group-title {
  color: #e2e8f0;
}

.section-group-title svg {
  color: var(--primary);
  flex-shrink: 0;
}

.section-group-hint {
  font-size: 0.76rem;
  color: var(--text-secondary);
  font-weight: 400;
  line-height: 1.35;
}

.inset-grouped-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 18px;
  overflow: hidden;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.04);
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

[data-theme="light"] .inset-grouped-card {
  background: #ffffff;
  border: 1px solid #e2e8f0;
  box-shadow: 0 4px 20px rgba(15, 23, 42, 0.04);
}

@media (max-width: 859px) {
  body.subpage-view-active .app-header,
  body.subpage-view-active .bottom-nav {
    display: none !important;
  }

  body.subpage-view-active .tab-content-area {
    padding-bottom: max(var(--safe-bottom, 12px), 16px);
  }
}

/* ==========================================================================
   Navigation: Mobile Bottom Navigation Bar (< 860px)
   ========================================================================== */
.sidebar-header,
.sidebar-footer {
  display: none;
}

.bottom-nav {
  order: 3;
  flex-shrink: 0;
  position: relative;
  bottom: auto;
  left: auto;
  transform: none;
  width: 100%;
  max-width: 480px;
  height: calc(64px + var(--safe-bottom));
  padding: 6px 14px var(--safe-bottom) 14px;
  background: var(--bg-glass);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 20px;
  z-index: 50;
  box-sizing: border-box;
}

.sidebar-nav-list {
  display: contents;
}

.nav-item {
  flex: 1;
  max-width: 160px;
  min-width: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  background: transparent;
  border: none;
  border-radius: 14px;
  color: var(--text-secondary);
  cursor: pointer;
  padding: 6px 12px;
  transition: all 0.22s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  -webkit-tap-highlight-color: transparent;
}

.nav-item:hover {
  color: var(--text-primary);
}

.nav-item .nav-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  color: inherit;
  transition: all 0.22s cubic-bezier(0.4, 0, 0.2, 1);
}

.nav-item .nav-icon svg {
  width: 22px;
  height: 22px;
  stroke: currentColor;
  stroke-width: 2.1;
  transition: all 0.22s ease;
}

.nav-item .nav-label {
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.01em;
  color: inherit;
  transition: all 0.2s ease;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 100%;
}

.nav-item.active {
  color: var(--primary);
  background: rgba(99, 102, 241, 0.08);
}

[data-theme="light"] .nav-item.active {
  color: #4f46e5;
  background: rgba(79, 70, 229, 0.08);
}

.nav-item.active .nav-icon {
  transform: translateY(-1px) scale(1.04);
}

.nav-item.active .nav-icon svg {
  stroke: var(--primary);
  stroke-width: 2.4;
  filter: drop-shadow(0 2px 6px rgba(99, 102, 241, 0.35));
}

[data-theme="light"] .nav-item.active .nav-icon svg {
  stroke: #4f46e5;
  filter: drop-shadow(0 2px 6px rgba(79, 70, 229, 0.35));
}

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

.sidebar-search-wrap {
  display: none;
}



/* ==========================================================================
   🖥️ DESKTOP & PC LAYOUT (>= 860px) - Dedicated Left Sidebar + Right Content
   ========================================================================== */
@media (min-width: 860px) {
  /* App Container: Full Desktop Dashboard Frame */
  #app-container {
    max-width: 100%;
    width: 100%;
    height: 100vh;
    height: 100dvh;
    max-height: 100vh;
    max-height: 100dvh;
    margin: 0;
    display: flex;
    flex-direction: row;
    align-items: stretch;
    box-shadow: none;
    background-color: var(--bg-primary);
    overflow: hidden;
  }

  /* Ẩn Header Mobile trên Desktop */
  .app-header {
    display: none !important;
  }

  /* Chuyển Bottom Nav thành Left Sidebar */
  .app-sidebar.bottom-nav {
    order: -1;
    position: relative;
    top: 0;
    left: 0;
    transform: none;
    width: 250px;
    min-width: 250px;
    max-width: 250px;
    height: 100%;
    max-height: 100%;
    padding: 20px 14px 16px 14px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    align-items: stretch;
    background: var(--bg-secondary);
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
    border-top: none;
    border-right: 1px solid var(--border);
    box-shadow: 2px 0 20px rgba(0, 0, 0, 0.08);
    z-index: 100;
    overflow-y: auto;
    overflow-x: hidden;
    scrollbar-width: thin;
  }

  [data-theme="light"] .app-sidebar.bottom-nav {
    background: #ffffff;
    border-right: 1px solid #e2e8f0;
    box-shadow: 2px 0 16px rgba(15, 23, 42, 0.03);
  }

  /* Sidebar Header Brand */
  .sidebar-header {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 0 4px 16px 4px;
    border-bottom: 1px solid var(--border);
    margin-bottom: 12px;
  }

  [data-theme="light"] .sidebar-header {
    border-bottom: 1px solid #f1f5f9;
  }

  /* Quick Search Widget on Desktop Sidebar */
  .sidebar-search-wrap {
    display: block;
    margin-bottom: 12px;
    padding: 0 2px;
  }

  .sidebar-search-btn {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 8px;
    padding: 9px 12px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: 11px;
    color: var(--text-secondary);
    font-size: 0.82rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  }

  [data-theme="light"] .sidebar-search-btn {
    background: #f1f5f9;
    border-color: #e2e8f0;
    color: #64748b;
  }

  .sidebar-search-btn:hover {
    border-color: var(--primary);
    color: var(--primary);
    background: rgba(99, 102, 241, 0.08);
    transform: translateY(-1px);
  }

  [data-theme="light"] .sidebar-search-btn:hover {
    background: #eff6ff;
    border-color: #a5b4fc;
    color: #4f46e5;
  }

  .search-kbd {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 5px;
    padding: 2px 6px;
    font-size: 0.66rem;
    font-family: var(--font-mono);
    color: var(--text-muted);
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
  }

  [data-theme="light"] .search-kbd {
    background: #ffffff;
    border-color: #cbd5e1;
    color: #475569;
  }



  .sidebar-brand-info {
    display: flex;
    flex-direction: column;
    gap: 2px;
  }

  .sidebar-brand-title {
    font-size: 1.08rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    color: var(--text-primary);
    line-height: 1.2;
  }

  /* Sidebar Navigation List */
  .sidebar-nav-list {
    display: flex;
    flex-direction: column;
    gap: 6px;
    flex: 1;
  }

  /* Nav Item trên Desktop (Dạng hàng ngang) */
  .nav-item {
    flex: none;
    width: 100%;
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: flex-start;
    gap: 12px;
    padding: 11px 16px;
    border-radius: 12px;
    font-size: 0.92rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-align: left;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    border-left: 3.5px solid transparent;
  }

  .nav-item .nav-icon {
    width: 22px;
    height: 22px;
    transform: none !important;
  }

  .nav-item .nav-icon svg {
    width: 20px;
    height: 20px;
    stroke-width: 2.2;
  }

  .nav-item .nav-label {
    font-size: 0.92rem;
    font-weight: 600;
    letter-spacing: -0.01em;
  }

  .nav-item:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    transform: translateX(2px);
  }

  [data-theme="light"] .nav-item:hover {
    background: #f1f5f9;
    color: #0f172a;
  }

  .nav-item.active {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.16), rgba(6, 182, 212, 0.08));
    color: var(--primary);
    font-weight: 700;
    border-left-color: var(--primary);
    transform: none;
  }

  [data-theme="light"] .nav-item.active {
    background: #eff6ff;
    color: #4f46e5;
    border-left-color: #4f46e5;
  }

  .nav-item.active .nav-icon svg {
    stroke: var(--primary);
    filter: drop-shadow(0 2px 8px var(--primary-glow));
  }

  [data-theme="light"] .nav-item.active .nav-icon svg {
    stroke: #4f46e5;
    filter: none;
  }

  /* Sidebar Footer (Streak Card) */
  .sidebar-footer {
    display: flex;
    flex-direction: column;
    gap: 10px;
    padding: 12px 0 0 0;
    border-top: 1px solid var(--border);
    margin-top: auto;
    flex-shrink: 0;
  }

  [data-theme="light"] .sidebar-footer {
    border-top: 1px solid #f1f5f9;
  }

  .sidebar-streak-card {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px 12px;
    background: rgba(245, 158, 11, 0.1);
    border: 1px solid rgba(245, 158, 11, 0.25);
    border-radius: 12px;
    transition: transform 0.2s ease;
  }

  [data-theme="light"] .sidebar-streak-card {
    background: #fffbeb;
    border: 1px solid #fde68a;
  }

  .sidebar-streak-card:hover {
    transform: translateY(-2px);
  }

  .sidebar-streak-icon {
    font-size: 1.5rem;
    line-height: 1;
  }

  .sidebar-streak-info {
    display: flex;
    flex-direction: column;
    gap: 2px;
  }

  .sidebar-streak-title {
    font-size: 0.72rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.03em;
  }

  [data-theme="light"] .sidebar-streak-title {
    color: #92400e;
  }

  .sidebar-streak-val {
    font-size: 0.95rem;
    color: #fbbf24;
    font-weight: 800;
  }

  [data-theme="light"] .sidebar-streak-val {
    color: #d97706;
  }

  .sidebar-streak-val strong {
    font-family: var(--font-mono);
    font-size: 1.1rem;
  }

  /* Right Main Tab View Area with Smooth macOS Floating Scrollbar */
  .tab-content-area {
    flex: 1;
    min-width: 0;
    height: 100%;
    max-height: 100%;
    padding: 24px 28px 32px 28px;
    max-width: 100%;
    width: 100%;
    margin: 0;
    overflow-y: auto;
    overflow-x: hidden;
    box-sizing: border-box;
    scrollbar-width: thin;
    scrollbar-color: rgba(99, 102, 241, 0.25) transparent;
  }

  /* Cho phép màn hình Trang chủ Ôn tập tự động co giãn không bị thanh cuộn lồng */
  #tab-review.active {
    display: block;
    width: 100%;
    height: auto;
    overflow: visible;
  }

  /* macOS Style Floating Rounded Pill Scrollbar */
  .tab-content-area::-webkit-scrollbar,
  .subtopics-list-container::-webkit-scrollbar,
  .subtopic-words-list::-webkit-scrollbar,
  .modal-body::-webkit-scrollbar {
    width: 7px;
  }

  .tab-content-area::-webkit-scrollbar-track,
  .subtopics-list-container::-webkit-scrollbar-track,
  .subtopic-words-list::-webkit-scrollbar-track,
  .modal-body::-webkit-scrollbar-track {
    background: transparent;
  }

  .tab-content-area::-webkit-scrollbar-thumb,
  .subtopics-list-container::-webkit-scrollbar-thumb,
  .subtopic-words-list::-webkit-scrollbar-thumb,
  .modal-body::-webkit-scrollbar-thumb {
    background: rgba(99, 102, 241, 0.22);
    border-radius: 9999px;
    border: 1.5px solid transparent;
    background-clip: padding-box;
    transition: background-color 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  }

  [data-theme="light"] .tab-content-area::-webkit-scrollbar-thumb {
    background: rgba(99, 102, 241, 0.25);
    background-clip: padding-box;
  }

  .tab-content-area::-webkit-scrollbar-thumb:hover,
  .subtopics-list-container::-webkit-scrollbar-thumb:hover,
  .subtopic-words-list::-webkit-scrollbar-thumb:hover,
  .modal-body::-webkit-scrollbar-thumb:hover {
    background: rgba(99, 102, 241, 0.55);
    background-clip: padding-box;
  }

  .tab-content-area::-webkit-scrollbar-thumb:active {
    background: var(--primary);
    background-clip: padding-box;
  }

  .tab-pane {
    padding: 0;
    max-width: 100%;
    width: 100%;
  }

  #tab-review.active {
    display: block;
    width: 100%;
  }
}


/* ==========================================================================
   FSRS-6 Flashcard Pro - Animations & Micro-interactions
   ========================================================================== */

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

@keyframes slideDownToast {
  from {
    opacity: 0;
    transform: translateY(-20px) scale(0.9);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

/* Card flip transition smoothing */
.flashcard-3d-wrapper {
  will-change: transform;
}

/* Smooth Tab Transition */
.tab-pane.active {
  animation: fadeIn 0.28s cubic-bezier(0.16, 1, 0.3, 1);
}

/* Universal Vietnam Flag Icon */
.flag-icon-vn {
  width: 18px;
  height: 12px;
  border-radius: 2.5px;
  vertical-align: -1.5px;
  display: inline-block;
  margin-right: 5px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
  flex-shrink: 0;
}