/* ========================================
   QUIZIZZ DESIGN SYSTEM v2.0
   Premium Glassmorphism UI with 3 Themes
   ======================================== */

/* ========================================
   1. CSS VARIABLES - THEME SYSTEM
   ======================================== */

/* 1.1 Light Theme (Default) */
:root {
  /* Background Colors */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --bg-page: #f5f3ff;

  /* Text Colors */
  --text-primary: #1e293b;
  --text-secondary: #64748b;
  --text-muted: #94a3b8;

  /* Accent Colors */
  --accent: #9333ea;
  --accent-hover: #7c3aed;
  --accent-light: #f3e8ff;

  /* Header */
  --header-bg: linear-gradient(135deg, #9333ea 0%, #7c3aed 100%);
  --header-text: #ffffff;

  /* Cards */
  --card-bg: rgba(255, 255, 255, 0.9);
  --card-border: rgba(0, 0, 0, 0.08);
  --card-shadow: 0 4px 20px rgba(0, 0, 0, 0.08);

  /* Glass Effect */
  --glass-bg: rgba(255, 255, 255, 0.7);
  --glass-border: rgba(255, 255, 255, 0.5);
  --glass-blur: 20px;

  /* Options */
  --option-border: #e2e8f0;
  --option-bg: #ffffff;
  --option-bg-hover: #f8fafc;
  --option-letter-bg: #f1f5f9;
  --option-text: #1e293b;
  --option-text-secondary: #475569;

  /* Option Colors (Quizizz Classic) */
  --option-red: #ef4444;
  --option-red-light: #fef2f2;
  --option-blue: #3b82f6;
  --option-blue-light: #eff6ff;
  --option-green: #22c55e;
  --option-green-light: #f0fdf4;
  --option-yellow: #eab308;
  --option-yellow-light: #fefce8;

  /* Selection & States */
  --selected-border: #9333ea;
  --selected-bg: #f3e8ff;

  /* Answer Feedback */
  --correct-bg: #dcfce7;
  --correct-border: #22c55e;
  --correct-text: #166534;
  --correct-icon: #22c55e;
  --wrong-bg: #fee2e2;
  --wrong-border: #ef4444;
  --wrong-text: #991b1b;
  --wrong-icon: #ef4444;

  /* Buttons */
  --btn-primary-bg: linear-gradient(135deg, #9333ea 0%, #7c3aed 100%);
  --btn-primary-hover: linear-gradient(135deg, #7c3aed 0%, #6d28d9 100%);
  --btn-submit-bg: linear-gradient(135deg, #22c55e 0%, #16a34a 100%);
  --btn-submit-hover: linear-gradient(135deg, #16a34a 0%, #15803d 100%);

  /* Progress */
  --progress-bg: #e2e8f0;
  --progress-bar: linear-gradient(90deg, #9333ea 0%, #ec4899 100%);

  /* Timer */
  --timer-bg: #5b21b6;
  --timer-text: #ffffff;

  /* Modal */
  --modal-overlay: rgba(0, 0, 0, 0.5);
  --modal-bg: rgba(255, 255, 255, 0.95);

  /* Misc */
  --divider: #e2e8f0;
  --scrollbar-thumb: #cbd5e1;
  --scrollbar-track: #f1f5f9;

  /* Blobs */
  --blob-1: rgba(147, 51, 234, 0.3);
  --blob-2: rgba(236, 72, 153, 0.2);
  --blob-3: rgba(59, 130, 246, 0.2);
}

/* 1.2 Dark Theme */
.theme-dark {
  /* Background Colors */
  --bg-primary: #0f0d1a;
  --bg-secondary: #1e1b2e;
  --bg-tertiary: #2d2a42;
  --bg-page: #0f0d1a;

  /* Text Colors */
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;

  /* Accent Colors */
  --accent: #a855f7;
  --accent-hover: #9333ea;
  --accent-light: #3b0764;

  /* Header */
  --header-bg: linear-gradient(135deg, #4c1d95 0%, #3b0764 100%);
  --header-text: #ffffff;

  /* Cards */
  --card-bg: rgba(30, 27, 46, 0.9);
  --card-border: rgba(255, 255, 255, 0.1);
  --card-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);

  /* Glass Effect */
  --glass-bg: rgba(30, 27, 46, 0.8);
  --glass-border: rgba(255, 255, 255, 0.1);
  --glass-blur: 20px;

  /* Options */
  --option-border: #374151;
  --option-bg: rgba(45, 42, 66, 0.8);
  --option-bg-hover: rgba(55, 52, 76, 0.9);
  --option-letter-bg: rgba(255, 255, 255, 0.1);
  --option-text: #ffffff;
  --option-text-secondary: #e2e8f0;

  /* Option Colors (Vibrant for Dark) */
  --option-red: #f87171;
  --option-red-light: rgba(248, 113, 113, 0.2);
  --option-blue: #60a5fa;
  --option-blue-light: rgba(96, 165, 250, 0.2);
  --option-green: #4ade80;
  --option-green-light: rgba(74, 222, 128, 0.2);
  --option-yellow: #facc15;
  --option-yellow-light: rgba(250, 204, 21, 0.2);

  /* Selection & States */
  --selected-border: #a855f7;
  --selected-bg: rgba(168, 85, 247, 0.2);

  /* Answer Feedback */
  --correct-bg: rgba(34, 197, 94, 0.3);
  --correct-border: #22c55e;
  --correct-text: #ffffff;
  --correct-icon: #4ade80;
  --wrong-bg: rgba(239, 68, 68, 0.3);
  --wrong-border: #ef4444;
  --wrong-text: #ffffff;
  --wrong-icon: #f87171;

  /* Buttons */
  --btn-primary-bg: linear-gradient(135deg, #7c3aed 0%, #6d28d9 100%);
  --btn-primary-hover: linear-gradient(135deg, #9333ea 0%, #7c3aed 100%);
  --btn-submit-bg: linear-gradient(135deg, #16a34a 0%, #15803d 100%);
  --btn-submit-hover: linear-gradient(135deg, #22c55e 0%, #16a34a 100%);

  /* Progress */
  --progress-bg: rgba(255, 255, 255, 0.1);
  --progress-bar: linear-gradient(90deg, #a855f7 0%, #ec4899 100%);

  /* Timer */
  --timer-bg: rgba(91, 33, 182, 0.8);
  --timer-text: #ffffff;

  /* Modal */
  --modal-overlay: rgba(0, 0, 0, 0.7);
  --modal-bg: rgba(30, 27, 46, 0.98);

  /* Misc */
  --divider: rgba(255, 255, 255, 0.1);
  --scrollbar-thumb: #4c1d95;
  --scrollbar-track: #1e1b2e;

  /* Blobs */
  --blob-1: rgba(147, 51, 234, 0.4);
  --blob-2: rgba(236, 72, 153, 0.3);
  --blob-3: rgba(59, 130, 246, 0.3);
}

/* 1.3 Purple Theme (Quizizz Classic) */
.theme-purple {
  /* Background Colors */
  --bg-primary: #5b21b6;
  --bg-secondary: #4c1d95;
  --bg-tertiary: #6d28d9;
  --bg-page: linear-gradient(180deg, #5b21b6 0%, #4c1d95 50%, #3b0764 100%);

  /* Text Colors */
  --text-primary: #ffffff;
  --text-secondary: #e9d5ff;
  --text-muted: #c4b5fd;

  /* Accent Colors */
  --accent: #fbbf24;
  --accent-hover: #f59e0b;
  --accent-light: rgba(251, 191, 36, 0.2);

  /* Header */
  --header-bg: linear-gradient(135deg, #4c1d95 0%, #3b0764 100%);
  --header-text: #ffffff;

  /* Cards */
  --card-bg: rgba(255, 255, 255, 0.1);
  --card-border: rgba(255, 255, 255, 0.2);
  --card-shadow: 0 4px 20px rgba(0, 0, 0, 0.2);

  /* Glass Effect */
  --glass-bg: rgba(255, 255, 255, 0.1);
  --glass-border: rgba(255, 255, 255, 0.2);
  --glass-blur: 20px;

  /* Options - Bold Quizizz Colors */
  --option-border: rgba(255, 255, 255, 0.3);
  --option-bg: rgba(255, 255, 255, 0.1);
  --option-bg-hover: rgba(255, 255, 255, 0.2);
  --option-letter-bg: rgba(255, 255, 255, 0.2);
  --option-text: #ffffff;
  --option-text-secondary: #f1f5f9;

  /* Option Colors (Quizizz Bold) */
  --option-red: #e12d39;
  --option-red-light: #e12d39;
  --option-blue: #2d70ae;
  --option-blue-light: #2d70ae;
  --option-green: #00a06a;
  --option-green-light: #00a06a;
  --option-yellow: #ff9800;
  --option-yellow-light: #ff9800;

  /* Selection & States */
  --selected-border: #fbbf24;
  --selected-bg: rgba(251, 191, 36, 0.3);

  /* Answer Feedback */
  --correct-bg: rgba(34, 197, 94, 0.4);
  --correct-border: #4ade80;
  --correct-text: #ffffff;
  --correct-icon: #4ade80;
  --wrong-bg: rgba(239, 68, 68, 0.4);
  --wrong-border: #f87171;
  --wrong-text: #ffffff;
  --wrong-icon: #f87171;

  /* Buttons */
  --btn-primary-bg: linear-gradient(135deg, #fbbf24 0%, #f59e0b 100%);
  --btn-primary-hover: linear-gradient(135deg, #f59e0b 0%, #d97706 100%);
  --btn-submit-bg: linear-gradient(135deg, #22c55e 0%, #16a34a 100%);
  --btn-submit-hover: linear-gradient(135deg, #16a34a 0%, #15803d 100%);

  /* Progress */
  --progress-bg: rgba(255, 255, 255, 0.2);
  --progress-bar: linear-gradient(90deg, #fbbf24 0%, #f59e0b 100%);

  /* Timer */
  --timer-bg: rgba(251, 191, 36, 0.9);
  --timer-text: #1e1b2e;

  /* Modal */
  --modal-overlay: rgba(0, 0, 0, 0.6);
  --modal-bg: rgba(76, 29, 149, 0.98);

  /* Misc */
  --divider: rgba(255, 255, 255, 0.2);
  --scrollbar-thumb: rgba(255, 255, 255, 0.3);
  --scrollbar-track: rgba(0, 0, 0, 0.2);

  /* Blobs */
  --blob-1: rgba(251, 191, 36, 0.3);
  --blob-2: rgba(236, 72, 153, 0.3);
  --blob-3: rgba(96, 165, 250, 0.3);
}

/* 1.4 Theme Transition - ⚡ PERFORMANCE: Chỉ áp dụng transition cho elements cần thiết */
/* Thay vì áp dụng cho tất cả *, chỉ áp dụng cho các elements thực sự cần animation khi đổi theme */
.glass-card,
.glass-header,
.option-card,
.btn-ghost,
.bg-secondary,
#quizizzContainer,
#questionContainer,
.progress-fill {
  transition:
    background-color 0.3s ease,
    border-color 0.3s ease,
    color 0.3s ease,
    box-shadow 0.3s ease;
}

/* Các elements cần transition nhanh hơn */
button,
.option-letter {
  transition:
    background-color 0.15s ease,
    transform 0.15s ease,
    box-shadow 0.15s ease;
}

/* Disable transitions khi reduce motion preference */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    transition: none !important;
    animation: none !important;
  }
}

html.theme-dark,
html.theme-purple {
  color-scheme: dark;
}

/* ========================================
   2. BASE STYLES
   ======================================== */

body {
  background: var(--bg-page);
  color: var(--text-primary);
  min-height: 100vh;
}

body.theme-dark {
  background: var(--bg-page);
}

body.theme-purple {
  background: var(--bg-page);
}

/* Custom Scrollbar */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--scrollbar-track);
}

::-webkit-scrollbar-thumb {
  background: var(--scrollbar-thumb);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--accent);
}

/* ========================================
   3. GLASSMORPHISM COMPONENTS
   ======================================== */

/* 3.1 Glass Card */
.glass-card {
  background: var(--glass-bg);
  backdrop-filter: blur(var(--glass-blur));
  -webkit-backdrop-filter: blur(var(--glass-blur));
  border: 1px solid var(--glass-border);
  border-radius: 16px;
  box-shadow: var(--card-shadow);
}

/* 3.2 Glass Header */
.glass-header {
  background: var(--header-bg);
  color: var(--header-text);
  padding: 1rem 1.5rem;
  border-radius: 16px 16px 0 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.glass-header h1 {
  font-size: 1.25rem;
  font-weight: 700;
  margin: 0;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

@media (max-width: 640px) {
  .glass-header {
    padding: 0.75rem 1rem;
  }

  .glass-header h1 {
    font-size: 1rem;
  }
}

/* 3.3 Glass Modal */
.glass-modal {
  background: var(--modal-bg);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border: 1px solid var(--glass-border);
  border-radius: 20px;
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
  max-width: 450px;
  width: 90%;
  max-height: 90vh;
  overflow-y: auto;
}

/* ========================================
   4. QUIZIZZ CONTAINER
   ======================================== */

#quizizzContainer {
  /* ⚡ PERFORMANCE: Chỉ transition properties cần thiết, tránh 'all' gây reflow */
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
  position: relative;
  z-index: 1;
}

#quizizzContainer > div {
  background-color: var(--card-bg);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: var(--card-shadow);
}

/* Header - First child */
#quizizzContainer > div > div:first-child {
  background: var(--header-bg);
  color: var(--header-text);
}

/* Info Panel - Second child */
#quizizzContainer > div > div:nth-child(2) {
  background-color: var(--bg-secondary);
  border-color: var(--divider);
  color: var(--text-primary);
}

/* Progress Container - Third child */
#quizizzContainer > div > div:nth-child(3) {
  background-color: var(--progress-bg);
}

/* ========================================
   5. OPTION CARDS
   ======================================== */

/* 5.1 Base Option Card */
.option-card {
  position: relative;
  background: var(--option-bg);
  border: 2px solid var(--option-border);
  border-radius: 12px;
  padding: 1rem 1.25rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  /* ⚡ PERFORMANCE: Chỉ transition properties cần thiết, GPU-friendly */
  transition:
    transform 0.2s ease,
    opacity 0.2s ease,
    background-color 0.2s ease,
    border-color 0.2s ease,
    box-shadow 0.2s ease;
  transform: translateY(0) translateZ(0); /* Force GPU compositing */
  will-change: transform, opacity;
  color: var(--option-text, var(--text-primary));
  /* ⚡ PERFORMANCE: Layout isolation - changes inside don't affect siblings */
  contain: layout style;
  /* 🛡️ FIX: Ngăn 300ms touch delay & double-tap-zoom trên mobile */
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  /* Prevent text selection khi tap nhanh */
  -webkit-user-select: none;
  user-select: none;
}

.option-card:hover {
  background-color: var(--option-bg-hover);
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgba(147, 51, 234, 0.15);
}

.option-card:active {
  transform: translateY(0) scale(0.98);
}

/* Option Letter Badge */
.option-card .option-letter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2rem;
  height: 2rem;
  border-radius: 8px;
  background-color: var(--option-letter-bg);
  margin-right: 0.875rem;
  font-weight: 600;
  font-size: 0.875rem;
  flex-shrink: 0;
  transition: all 0.2s ease;
}

/* 5.2 Color Variants */
.option-red {
  /* Color variant marker - hover styles below */
  --_option-accent: var(--option-red);
}

/* .option-red:hover {
  background-color: var(--option-red-light);
  border-color: var(--option-red);
} */

.option-red .option-letter {
  background-color: #e2e8f0;
  color: #1e293b;
}

.option-blue {
  /* Color variant marker - hover styles below */
  --_option-accent: var(--option-blue);
}

/* .option-blue:hover {
  background-color: var(--option-blue-light);
  border-color: var(--option-blue);
} */

.option-blue .option-letter {
  background-color: #e2e8f0;
  color: #1e293b;
}

.option-green {
  /* Color variant marker - hover styles below */
  --_option-accent: var(--option-green);
}

/* .option-green:hover {
  background-color: var(--option-green-light);
  border-color: var(--option-green);
} */

.option-green .option-letter {
  background-color: #e2e8f0;
  color: #1e293b;
}

.option-yellow {
  /* Color variant marker - hover styles below */
  --_option-accent: var(--option-yellow);
}

/* .option-yellow:hover {
  background-color: var(--option-yellow-light);
  border-color: var(--option-yellow);
} */

.option-yellow .option-letter {
  background-color: #e2e8f0;
  color: #1e293b;
}

/* 5.3 Selected State */
.option-card.selected {
  border-color: var(--selected-border);
  background-color: var(--selected-bg);
  transform: translateY(-2px) scale(1.01);
  box-shadow: 0 10px 30px rgba(147, 51, 234, 0.2);
}

.option-card.selected .option-letter {
  background-color: var(--accent);
  color: white;
}

/* 5.4 Correct/Wrong States */
.option-card.answer-correct,
.option-card.border-green-500 {
  background-color: var(--correct-bg) !important;
  border-color: var(--correct-border) !important;
  color: var(--correct-text) !important;
}

.option-card.answer-correct .option-letter {
  background-color: var(--correct-border);
  color: white;
}

.option-card.answer-wrong,
.option-card.border-red-500 {
  background-color: var(--wrong-bg) !important;
  border-color: var(--wrong-border) !important;
  color: var(--wrong-text) !important;
}

.option-card.answer-wrong .option-letter {
  background-color: var(--wrong-border);
  color: white;
}

/* Icons in options */
.option-card .text-green-600 {
  color: var(--correct-icon) !important;
}

.option-card .text-red-600 {
  color: var(--wrong-icon) !important;
}

/* 5.5 Purple Theme - Bold Quizizz Style Options */
.theme-purple .option-red {
  background-color: var(--option-red);
  border-color: var(--option-red);
  color: white;
}

.theme-purple .option-blue {
  background-color: var(--option-blue);
  border-color: var(--option-blue);
  color: white;
}

.theme-purple .option-green {
  background-color: var(--option-green);
  border-color: var(--option-green);
  color: white;
}

.theme-purple .option-yellow {
  background-color: var(--option-yellow);
  border-color: var(--option-yellow);
  color: white;
}

.theme-purple .option-card:hover {
  filter: brightness(1.1);
  transform: translateY(-3px);
}

.theme-purple .option-card .option-letter {
  background-color: rgba(255, 255, 255, 0.25);
  color: white;
}

/* Dark Theme Options */
.theme-dark .option-card {
  color: #ffffff;
}

.theme-dark .option-card .option-letter {
  color: #ffffff;
  background-color: rgba(255, 255, 255, 0.15);
}

.theme-dark .option-card:hover {
  box-shadow: 0 8px 25px rgba(168, 85, 247, 0.25);
}

.theme-dark .option-card.selected {
  box-shadow: 0 10px 30px rgba(168, 85, 247, 0.35);
}

/* ===== Dark/Purple Theme - Review Section Text Colors ===== */

/* Question text in review */
.theme-dark .text-gray-800,
.theme-purple .text-gray-800 {
  color: #ffffff !important;
}

.theme-dark .text-gray-600,
.theme-purple .text-gray-600 {
  color: #e2e8f0 !important;
}

/* Review item borders */
.theme-dark .border-gray-200,
.theme-purple .border-gray-200 {
  border-color: rgba(255, 255, 255, 0.2) !important;
}

/* Green text (correct answers) */
.theme-dark .text-green-800,
.theme-dark .text-green-600,
.theme-purple .text-green-800,
.theme-purple .text-green-600 {
  color: #4ade80 !important;
}

.theme-dark .bg-green-100,
.theme-purple .bg-green-100 {
  background-color: rgba(34, 197, 94, 0.3) !important;
}

.theme-dark .border-green-500,
.theme-purple .border-green-500 {
  border-color: #22c55e !important;
}

/* Red text (wrong answers) */
.theme-dark .text-red-800,
.theme-dark .text-red-600,
.theme-purple .text-red-800,
.theme-purple .text-red-600 {
  color: #f87171 !important;
}

.theme-dark .bg-red-100,
.theme-purple .bg-red-100 {
  background-color: rgba(239, 68, 68, 0.3) !important;
}

.theme-dark .border-red-500,
.theme-purple .border-red-500 {
  border-color: #ef4444 !important;
}

/* Review option letter badges */
.theme-dark .bg-purple-100,
.theme-purple .bg-purple-100 {
  background-color: rgba(168, 85, 247, 0.3) !important;
}

.theme-dark .text-purple-600,
.theme-purple .text-purple-600 {
  color: #c4b5fd !important;
}

/* Option text in Dark/Purple - force white when correct/wrong */
.theme-dark .option-card.answer-correct,
.theme-dark .option-card.answer-wrong,
.theme-purple .option-card.answer-correct,
.theme-purple .option-card.answer-wrong {
  color: #ffffff !important;
}

/* Review section container text */
.theme-dark #reviewContainer,
.theme-purple #reviewContainer {
  color: #ffffff;
}

.theme-dark #reviewContainer h4,
.theme-purple #reviewContainer h4 {
  color: #ffffff !important;
}

.theme-dark #reviewContainer .rounded,
.theme-purple #reviewContainer .rounded {
  color: #f1f5f9;
}

/* Selected options during quiz should have white text */
.theme-dark .option-card.selected,
.theme-purple .option-card.selected {
  color: #ffffff !important;
}

/* Mobile Options */
@media (max-width: 640px) {
  .option-card {
    padding: 0.875rem 1rem;
    border-radius: 10px;
  }

  .option-card .option-letter {
    width: 1.75rem;
    height: 1.75rem;
    font-size: 0.8rem;
    margin-right: 0.75rem;
  }

  .option-card:hover {
    transform: none;
    box-shadow: none;
  }
}

/* ========================================
   6. BUTTONS
   ======================================== */

/* 6.1 Primary Button */
.btn-primary {
  background: var(--btn-primary-bg);
  color: white;
  padding: 0.75rem 1.5rem;
  border-radius: 12px;
  font-weight: 600;
  font-size: 1rem;
  border: none;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  transition: all 0.25s ease;
  position: relative;
  overflow: hidden;
}

.btn-primary:hover {
  background: var(--btn-primary-hover);
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgba(147, 51, 234, 0.3);
}

.btn-primary:active {
  transform: translateY(0);
}

.theme-purple .btn-primary {
  color: #1e1b2e;
}

/* 6.2 Secondary Button */
.btn-secondary {
  background: transparent;
  color: var(--accent);
  padding: 0.75rem 1.5rem;
  border-radius: 12px;
  font-weight: 600;
  font-size: 1rem;
  border: 2px solid var(--accent);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  transition: all 0.25s ease;
}

.btn-secondary:hover {
  background: var(--accent);
  color: white;
  transform: translateY(-2px);
}

/* 6.3 Ghost Button */
.btn-ghost {
  background: transparent;
  color: inherit;
  padding: 0.5rem;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
}

.btn-ghost:hover {
  background: rgba(255, 255, 255, 0.1);
}

.btn-ghost:active {
  transform: scale(0.95);
}

/* 6.4 Button Group (Speed Selection) */
.btn-group {
  display: flex;
  gap: 0.25rem;
  background: var(--bg-tertiary);
  padding: 0.25rem;
  border-radius: 10px;
}

.btn-group button {
  flex: 1;
  padding: 0.5rem 0.75rem;
  border: none;
  background: transparent;
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.875rem;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s ease;
}

.btn-group button:hover {
  background: rgba(147, 51, 234, 0.1);
  color: var(--accent);
}

.btn-group button.active {
  background: var(--accent);
  color: white;
  box-shadow: 0 2px 8px rgba(147, 51, 234, 0.3);
}

.theme-dark .btn-group {
  background: rgba(255, 255, 255, 0.05);
}

.theme-purple .btn-group {
  background: rgba(0, 0, 0, 0.2);
}

.theme-purple .btn-group button.active {
  background: var(--accent);
  color: #1e1b2e;
}

/* Submit Button */
#submitExamButton {
  background: var(--btn-submit-bg);
  color: white;
  padding: 0.75rem 2rem;
  border-radius: 50px;
  font-weight: 600;
  font-size: 1rem;
  border: none;
  cursor: pointer;
  transition: all 0.25s ease;
}

#submitExamButton:hover {
  background: var(--btn-submit-hover);
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgba(34, 197, 94, 0.3);
}

/* Quiz Button (Legacy Support) */
.quiz-button {
  background: var(--btn-primary-bg);
  color: white;
  transition: all 0.24s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
}

.quiz-button:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 16px rgba(0, 0, 0, 0.15);
}

.quiz-button:active {
  transform: translateY(0);
}

/* Next/Finish Buttons */
#nextButton {
  background: var(--btn-primary-bg);
  color: white;
}

#nextButton:hover {
  background: var(--btn-primary-hover);
}

#finishButton {
  background: var(--btn-submit-bg);
  color: white;
}

#finishButton:hover {
  background: var(--btn-submit-hover);
}

/* ========================================
   7. PROGRESS BAR
   ======================================== */

#progressBar {
  background: var(--progress-bar);
  transition: width 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
  /* ⚡ PERFORMANCE: GPU layer for smooth width transitions */
  transform: translateZ(0);
  contain: layout style;
}

#progressBar::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: linear-gradient(
    90deg,
    transparent,
    rgba(255, 255, 255, 0.4),
    transparent
  );
  animation: progressShimmer 2s infinite;
  /* ⚡ PERFORMANCE: GPU accelerate shimmer */
  transform: translateZ(0);
  will-change: transform;
}

/* ========================================
   8. TIMER
   ======================================== */

#examTimer {
  background-color: var(--timer-bg);
  color: var(--timer-text);
  transition: all 0.3s ease;
}

#examTimer.quiz-timer-warning {
  animation: countdownPulse 0.5s ease-in-out infinite;
  background-color: #dc2626 !important;
}

#examTimer.quiz-timer-critical {
  animation: shake 0.3s ease-in-out infinite;
  background-color: #b91c1c !important;
}

/* ========================================
   9. MODAL STYLES
   ======================================== */

.modal-overlay {
  position: fixed;
  inset: 0;
  background: var(--modal-overlay);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 9999;
  opacity: 0;
  visibility: hidden;
  /* ⚡ PERFORMANCE: Chỉ transition opacity + visibility, GPU-accelerated */
  transition:
    opacity 0.3s ease,
    visibility 0.3s ease;
  transform: translateZ(0); /* Force GPU compositing layer */
  will-change: opacity;
}

.modal-overlay.show {
  opacity: 1;
  visibility: visible;
}

.modal-overlay.hidden {
  display: none;
}

.modal-content {
  /* ⚡ PERFORMANCE: GPU-accelerated transform + opacity */
  transform: scale(0.9) translateY(20px) translateZ(0);
  opacity: 0;
  transition:
    transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1),
    opacity 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
  will-change: transform, opacity;
}

.modal-overlay.show .modal-content {
  transform: scale(1) translateY(0) translateZ(0);
  opacity: 1;
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.25rem 1.5rem;
  border-bottom: 1px solid var(--divider);
}

.modal-header h2 {
  font-size: 1.25rem;
  font-weight: 700;
  margin: 0;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--text-primary);
}

.modal-body {
  padding: 1.5rem;
}

.modal-footer {
  padding: 1rem 1.5rem;
  border-top: 1px solid var(--divider);
  display: flex;
  justify-content: flex-end;
  gap: 0.75rem;
}

/* Settings Section */
.settings-section {
  margin-bottom: 1.5rem;
}

.settings-section:last-child {
  margin-bottom: 0;
}

.section-label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
}

/* Toggle Switch */
.toggle-container {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.toggle-switch {
  position: relative;
  display: inline-block;
  width: 52px;
  height: 28px;
}

.toggle-switch input {
  opacity: 0;
  width: 0;
  height: 0;
}

.toggle-slider {
  position: absolute;
  cursor: pointer;
  inset: 0;
  background-color: var(--bg-tertiary);
  border-radius: 28px;
  transition: all 0.3s ease;
}

.toggle-slider::before {
  content: "";
  position: absolute;
  width: 22px;
  height: 22px;
  left: 3px;
  bottom: 3px;
  background-color: white;
  border-radius: 50%;
  transition: all 0.3s ease;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.toggle-switch input:checked + .toggle-slider {
  background: var(--accent);
}

.toggle-switch input:checked + .toggle-slider::before {
  transform: translateX(24px);
}

/* Theme Cards */
.theme-options {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
}

.theme-card {
  background: var(--bg-tertiary);
  border: 2px solid transparent;
  border-radius: 12px;
  padding: 0.75rem;
  cursor: pointer;
  text-align: center;
  transition: all 0.25s ease;
}

.theme-card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
}

.theme-card.active {
  border-color: var(--accent);
  background: var(--accent-light);
}

.theme-preview {
  width: 100%;
  height: 40px;
  border-radius: 8px;
  margin-bottom: 0.5rem;
}

.theme-preview-light {
  background: linear-gradient(135deg, #ffffff 0%, #f8fafc 100%);
  border: 1px solid #e2e8f0;
}

.theme-preview-dark {
  background: linear-gradient(135deg, #1e1b2e 0%, #0f0d1a 100%);
}

.theme-preview-purple {
  background: linear-gradient(135deg, #7c3aed 0%, #5b21b6 100%);
}

.theme-card span {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-primary);
}

/* ========================================
   10. FLOATING BLOBS (Background)
   ======================================== */
/* NOTE: Canonical blob declarations - Section 20.2 overrides removed */

.blobs-container {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  overflow: hidden;
  /* ⚡ PERFORMANCE: Isolate from main content rendering */
  contain: strict;
}

.blob {
  position: absolute;
  border-radius: 50%;
  filter: blur(80px);
  opacity: 0.6;
  animation: blobFloat 25s ease-in-out infinite;
  /* ⚡ PERFORMANCE: GPU compositing for blob animations */
  will-change: transform;
  transform: translateZ(0);
}

.blob-1 {
  width: 400px;
  height: 400px;
  background: var(--blob-1);
  top: -100px;
  right: -100px;
}

.blob-2 {
  width: 350px;
  height: 350px;
  background: var(--blob-2);
  bottom: -80px;
  left: -80px;
  animation-delay: -5s;
  animation-direction: reverse;
}

.blob-3 {
  width: 300px;
  height: 300px;
  background: var(--blob-3);
  top: 40%;
  left: 60%;
  animation-delay: -10s;
}

@keyframes blobFloat {
  0%,
  100% {
    transform: translate(0, 0) scale(1) translateZ(0);
  }
  33% {
    transform: translate(30px, -50px) scale(1.1) translateZ(0);
  }
  66% {
    transform: translate(-20px, 20px) scale(0.9) translateZ(0);
  }
}

/* Hide blobs on mobile/touch for performance */
@media (max-width: 768px), (hover: none) {
  .blobs-container {
    display: none;
  }
}

/* ========================================
   11. TYPOGRAPHY & UTILITIES
   ======================================== */

/* Headings */
.quiz-h1 {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 1rem;
}

.quiz-h2 {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
}

.quiz-h3 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

/* Text Colors */
.text-primary {
  color: var(--text-primary);
}
.text-secondary {
  color: var(--text-secondary);
}
.text-muted {
  color: var(--text-muted);
}
.text-accent {
  color: var(--accent);
}

/* Backgrounds */
.bg-primary {
  background-color: var(--bg-primary);
}
.bg-secondary {
  background-color: var(--bg-secondary);
}

/* Divider */
.divider {
  height: 1px;
  background: var(--divider);
  margin: 1rem 0;
}

/* Question Text */
#question-container h2,
#questionText {
  word-break: break-word;
  hyphens: auto;
  color: var(--text-primary);
}

/* ========================================
   12. QUESTION CONTAINER
   ======================================== */

.question-card {
  display: flex;
  flex-direction: column;
  height: 100%;
}

#question-container {
  display: flex;
  flex-direction: column;
  height: 100%;
  min-height: 0;
}

#options-container {
  margin-bottom: 0;
}

.option-button {
  display: flex;
  align-items: center;
  padding: 0.75rem;
  word-break: break-word;
  position: relative;
}

#exam-container {
  max-height: calc(100vh - 200px);
  min-height: 400px;
  display: flex;
  flex-direction: column;
}

#questionContainer {
  position: relative;
  overflow: hidden;
  background-color: var(--card-bg);
  color: var(--text-primary);
  /* ⚡ PERFORMANCE: Isolate question animations from rest of page */
  contain: layout style;
  transform: translateZ(0);
}

.quiz-question-container {
  transform: translateZ(0);
  backface-visibility: hidden;
}

.question-slide-transition {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  width: 100%;
}

/* ========================================
   13. RESULT DISPLAY
   ======================================== */

.result-display {
  transition: all 0.3s ease;
  color: var(--text-primary);
}

.result-display h2,
.result-display h3,
.result-display h4 {
  color: var(--text-primary);
}

.theme-dark .result-display .text-purple-600,
.theme-purple .result-display .text-purple-600 {
  color: var(--accent) !important;
}

.theme-dark .result-display .bg-purple-100,
.theme-purple .result-display .bg-purple-100 {
  background-color: var(--accent-light) !important;
}

.theme-dark .result-display .text-gray-600,
.theme-dark .result-display .text-gray-700,
.theme-dark .result-display .text-gray-800 {
  color: var(--text-secondary) !important;
}

.theme-dark .result-display .bg-gray-50 {
  background-color: var(--bg-secondary) !important;
}

.theme-dark .result-display .border-gray-200 {
  border-color: var(--divider) !important;
}

.theme-dark .result-display h3 {
  color: var(--text-primary) !important;
}

/* Result - Correct/Wrong in dark mode */
.theme-dark .result-display .bg-green-100,
.theme-purple .result-display .bg-green-100 {
  background-color: var(--correct-bg) !important;
  color: var(--correct-text) !important;
  border-color: var(--correct-border) !important;
}

.theme-dark .result-display .bg-red-100,
.theme-purple .result-display .bg-red-100 {
  background-color: var(--wrong-bg) !important;
  color: var(--wrong-text) !important;
  border-color: var(--wrong-border) !important;
}

.theme-dark .result-display .text-red-800,
.theme-purple .result-display .text-red-800 {
  color: var(--wrong-text) !important;
}

.theme-dark .result-display .text-green-800,
.theme-purple .result-display .text-green-800 {
  color: var(--correct-text) !important;
}

/* ========================================
   14. SECURITY WARNING
   ======================================== */

.theme-dark .security-warning {
  background-color: var(--bg-secondary);
}

.theme-dark .security-warning-title {
  color: #ef4444;
}

.theme-dark .security-warning-message {
  color: var(--text-primary);
}

.theme-dark .security-warning-btn {
  background-color: #dc2626;
}

.theme-dark .security-warning-btn:hover {
  background-color: #b91c1c;
}

/* ========================================
   15. DROPDOWN (Legacy Support)
   ======================================== */

#transitionTime {
  background-color: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.3);
  color: white;
  border-radius: 6px;
  padding: 0.25rem 0.5rem;
  font-size: 0.875rem;
}

#transitionTime option {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
}

/* Toggle Buttons (Legacy) */
#soundToggleBtn,
#themeToggleBtn {
  cursor: pointer;
  transition: all 0.2s;
}

#soundToggleBtn:hover,
#themeToggleBtn:hover {
  opacity: 0.8;
  transform: scale(1.1);
}

/* ========================================
   16. LOADING STATES
   ======================================== */

.quiz-loading-container {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 200px;
}

.quiz-spinner {
  width: 40px;
  height: 40px;
  border: 4px solid var(--divider);
  border-top: 4px solid var(--accent);
  border-radius: 50%;
  animation: loading 1s linear infinite;
}

.quiz-success-icon {
  color: var(--correct-icon);
  animation: bounceIn 0.6s ease-out;
}

.quiz-error-icon {
  color: var(--wrong-icon);
  animation: shake 0.6s ease-out;
}

/* ========================================
   17. KEYFRAME ANIMATIONS
   ======================================== */

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideInLeft {
  from {
    opacity: 0;
    transform: translateX(-100px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes slideInRight {
  from {
    opacity: 0;
    transform: translateX(100px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes slideOutLeft {
  from {
    opacity: 1;
    transform: translateX(0);
  }
  to {
    opacity: 0;
    transform: translateX(-100px);
  }
}

@keyframes slideOutRight {
  from {
    opacity: 1;
    transform: translateX(0);
  }
  to {
    opacity: 0;
    transform: translateX(100px);
  }
}

@keyframes bounceIn {
  0% {
    opacity: 0;
    transform: scale(0.3) translateY(-20px);
  }
  50% {
    opacity: 1;
    transform: scale(1.05) translateY(0);
  }
  70% {
    transform: scale(0.95);
  }
  100% {
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes pulse {
  0% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.02);
  }
  100% {
    transform: scale(1);
  }
}

@keyframes gentleScale {
  0% {
    transform: scale(1) translateZ(0);
  }
  50% {
    transform: scale(1.01) translateZ(0);
  }
  100% {
    transform: scale(1) translateZ(0);
  }
}

@keyframes gentleShakeScale {
  0% {
    transform: scale(1) translateX(0);
  }
  25% {
    transform: scale(1.02) translateX(-2px);
  }
  50% {
    transform: scale(1.03) translateX(2px);
  }
  75% {
    transform: scale(1.02) translateX(-1px);
  }
  100% {
    transform: scale(1.02) translateX(0);
  }
}

@keyframes zoomIn {
  from {
    opacity: 0;
    transform: scale(0.8);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes zoomOut {
  from {
    opacity: 1;
    transform: scale(1);
  }
  to {
    opacity: 0;
    transform: scale(0.8);
  }
}

@keyframes popIn {
  0% {
    opacity: 0;
    transform: scale(0.5) rotate(-10deg);
  }
  50% {
    opacity: 1;
    transform: scale(1.1) rotate(5deg);
  }
  100% {
    opacity: 1;
    transform: scale(1) rotate(0deg);
  }
}

@keyframes slideUp {
  from {
    opacity: 0;
    transform: translateY(50px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideDown {
  from {
    opacity: 1;
    transform: translateY(0);
  }
  to {
    opacity: 0;
    transform: translateY(50px);
  }
}

@keyframes correctAnswer {
  0% {
    background-color: var(--option-bg-hover);
    transform: scale(1) translateZ(0);
  }
  50% {
    background-color: var(--correct-bg);
    transform: scale(1.01) translateZ(0);
  }
  100% {
    background-color: var(--correct-bg);
    transform: scale(1) translateZ(0);
  }
}

@keyframes wrongAnswer {
  0% {
    background-color: var(--option-bg-hover);
    transform: translateX(0) translateZ(0);
  }
  20% {
    background-color: var(--wrong-bg);
    transform: translateX(-1px) translateZ(0);
  }
  40% {
    transform: translateX(1px) translateZ(0);
  }
  60% {
    transform: translateX(-1px) translateZ(0);
  }
  80% {
    transform: translateX(1px) translateZ(0);
  }
  100% {
    background-color: var(--wrong-bg);
    transform: translateX(0) translateZ(0);
  }
}

@keyframes celebration {
  0%,
  100% {
    transform: scale(1) rotate(0deg);
  }
  25% {
    transform: scale(1.1) rotate(-5deg);
  }
  50% {
    transform: scale(1.2) rotate(5deg);
  }
  75% {
    transform: scale(1.1) rotate(-2deg);
  }
}

@keyframes loading {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}

@keyframes countdownPulse {
  0% {
    transform: scale(1);
    opacity: 1;
  }
  50% {
    transform: scale(1.1);
    opacity: 0.8;
  }
  100% {
    transform: scale(1);
    opacity: 1;
  }
}

@keyframes progressShimmer {
  0% {
    transform: translateX(-100%);
  }
  100% {
    transform: translateX(100%);
  }
}

@keyframes flipIn {
  0% {
    opacity: 0;
    transform: rotateY(-90deg);
  }
  100% {
    opacity: 1;
    transform: rotateY(0);
  }
}

@keyframes flipOut {
  0% {
    opacity: 1;
    transform: rotateY(0);
  }
  100% {
    opacity: 0;
    transform: rotateY(90deg);
  }
}

@keyframes shake {
  0%,
  100% {
    transform: translateX(0);
  }
  25% {
    transform: translateX(-5px);
  }
  75% {
    transform: translateX(5px);
  }
}

/* ========================================
   18. ANIMATION CLASSES
   ======================================== */

.quiz-fade-in {
  animation: fadeIn 0.5s ease-out forwards;
}
.quiz-slide-in-left {
  animation: slideInLeft 0.5s ease-out forwards;
}
.quiz-slide-in-right {
  animation: slideInRight 0.5s ease-out forwards;
}
.quiz-slide-out-left {
  animation: slideOutLeft 0.4s ease-in forwards;
}
.quiz-slide-out-right {
  animation: slideOutRight 0.4s ease-in forwards;
}
.quiz-bounce-in {
  animation: bounceIn 0.6s ease-out forwards;
}
.quiz-pulse {
  animation: pulse 1s ease-in-out infinite;
}
.quiz-gentle-scale {
  animation: gentleScale 0.4s ease-out forwards;
}
.quiz-gentle-shake-scale {
  animation: gentleShakeScale 0.5s ease-out forwards;
}
.quiz-zoom-in {
  animation: zoomIn 0.2s ease-out forwards;
}
.quiz-zoom-out {
  animation: zoomOut 0.3s ease-in forwards;
}
.quiz-pop-in {
  animation: popIn 0.4s cubic-bezier(0.68, -0.55, 0.265, 1.55) forwards;
}
.quiz-slide-up {
  animation: slideUp 0.4s ease-out forwards;
}
.quiz-slide-down {
  animation: slideDown 0.3s ease-in forwards;
}
.quiz-correct-answer {
  animation: correctAnswer 0.6s ease-out forwards;
}
.quiz-wrong-answer {
  animation: wrongAnswer 0.6s ease-out forwards;
}
.quiz-celebration {
  animation: celebration 0.8s ease-in-out;
}
.quiz-loading {
  animation: loading 1s linear infinite;
}
.quiz-countdown-pulse {
  animation: countdownPulse 0.8s ease-in-out infinite;
}
.quiz-flip-in {
  animation: flipIn 0.5s ease-out forwards;
}
.quiz-flip-out {
  animation: flipOut 0.3s ease-in forwards;
}

/* ⚡ FIX: quiz-fade-out was used in JS but never defined in CSS */
@keyframes fadeOut {
  from {
    opacity: 1;
    transform: scale(1) translateZ(0);
  }
  to {
    opacity: 0;
    transform: scale(0.95) translateZ(0);
  }
}
.quiz-fade-out {
  animation: fadeOut 0.3s ease-out forwards;
  pointer-events: none; /* Prevent clicks during fade */
}

/* Stagger Delays */
.quiz-stagger-1 {
  animation-delay: 0.1s;
}
.quiz-stagger-2 {
  animation-delay: 0.2s;
}
.quiz-stagger-3 {
  animation-delay: 0.3s;
}
.quiz-stagger-4 {
  animation-delay: 0.4s;
}
.quiz-stagger-5 {
  animation-delay: 0.5s;
}

/* Transition Classes */
.quiz-transition {
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}
.quiz-transition-fast {
  transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}
.quiz-transition-slow {
  transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}
.quiz-transform-gpu {
  transform: translateZ(0);
  will-change: transform, opacity;
}

.quiz-answer-reveal {
  opacity: 0;
  animation: fadeIn 0.5s ease-out forwards;
}

/* ========================================
   19. RESPONSIVE STYLES
   ======================================== */

@media (max-width: 768px) {
  /* Reduce animations on mobile */
  .quiz-transition {
    transition: all 0.2s ease;
  }

  .quiz-fade-in,
  .quiz-slide-in-left,
  .quiz-slide-in-right {
    animation-duration: 0.3s;
  }

  /* Simpler hover effects on mobile */
  .option-card:hover {
    background-color: var(--option-bg-hover);
    transform: none;
    box-shadow: none;
  }

  .quiz-button:hover {
    transform: none;
  }

  /* Modal responsive */
  .glass-modal {
    max-width: 95%;
    max-height: 85vh;
  }

  .theme-options {
    gap: 0.5rem;
  }

  .btn-group button {
    padding: 0.4rem 0.5rem;
    font-size: 0.8rem;
  }
}

/* ========================================
   20. ANIMATIONS & KEYFRAMES
   ======================================== */

/* 20.1 Keyframe Definitions */

/* Floating blob animation */
@keyframes blob-float {
  0%,
  100% {
    transform: translate(0, 0) scale(1) rotate(0deg);
  }
  33% {
    transform: translate(30px, -50px) scale(1.1) rotate(10deg);
  }
  66% {
    transform: translate(-20px, 20px) scale(0.9) rotate(-10deg);
  }
}

/* Question slide in from right */
@keyframes slide-in-right {
  from {
    opacity: 0;
    transform: translateX(50px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* Question slide in from left */
@keyframes slide-in-left {
  from {
    opacity: 0;
    transform: translateX(-50px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* Fade up animation */
@keyframes fade-up {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Fade in */
@keyframes fade-in {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

/* Correct answer bounce */
@keyframes bounce-correct {
  0%,
  100% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.03);
  }
}

/* Wrong answer shake */
@keyframes shake-wrong {
  0%,
  100% {
    transform: translateX(0);
  }
  10%,
  30%,
  50%,
  70%,
  90% {
    transform: translateX(-4px);
  }
  20%,
  40%,
  60%,
  80% {
    transform: translateX(4px);
  }
}

/* Modal open animation */
@keyframes modal-open {
  from {
    opacity: 0;
    transform: scale(0.95) translateY(-10px);
  }
  to {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
}

/* Modal close animation */
@keyframes modal-close {
  from {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
  to {
    opacity: 0;
    transform: scale(0.95) translateY(-10px);
  }
}

/* Pulse animation */
@keyframes pulse {
  0%,
  100% {
    opacity: 1;
  }
  50% {
    opacity: 0.7;
  }
}

/* Pulse scale animation */
@keyframes pulse-scale {
  0%,
  100% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.02);
  }
}

/* Progress bar shimmer */
@keyframes progress-shimmer {
  0% {
    background-position: -200% 0;
  }
  100% {
    background-position: 200% 0;
  }
}

/* Countdown flash */
@keyframes countdown-flash {
  0%,
  100% {
    background: var(--timer-bg);
    color: var(--timer-text);
  }
  50% {
    background: #ef4444;
    color: white;
    transform: scale(1.05);
  }
}

/* Settings icon rotate */
@keyframes icon-rotate {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(180deg);
  }
}

/* Stagger delay helper classes */
.stagger-1 {
  animation-delay: 0.05s;
}
.stagger-2 {
  animation-delay: 0.1s;
}
.stagger-3 {
  animation-delay: 0.15s;
}
.stagger-4 {
  animation-delay: 0.2s;
}

/* 20.2 Floating Blobs Background — REMOVED DUPLICATE */
/* ⚡ PERFORMANCE: Canonical blob declarations in Section 10 above */

/* 20.3 Question Transition Animations */
.quiz-slide-in {
  animation: slide-in-right 0.4s cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

.quiz-slide-in-reverse {
  animation: slide-in-left 0.4s cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

.quiz-fade-up {
  animation: fade-up 0.3s ease-out forwards;
}

/* 20.4 Option Card Animations — CONSOLIDATED */
/* ⚡ PERFORMANCE: Base .option-card transition now in Section 5.1 (single source of truth) */

.option-card.selected-pulse {
  animation: pulse-scale 0.3s ease;
}

.option-card.correct-bounce {
  animation: bounce-correct 0.5s ease;
}

.option-card.wrong-shake {
  animation: shake-wrong 0.5s ease;
}

/* Option stagger animation on load */
.option-card.animate-in:nth-child(1) {
  animation: fade-up 0.3s ease-out 0.05s backwards;
}
.option-card.animate-in:nth-child(2) {
  animation: fade-up 0.3s ease-out 0.1s backwards;
}
.option-card.animate-in:nth-child(3) {
  animation: fade-up 0.3s ease-out 0.15s backwards;
}
.option-card.animate-in:nth-child(4) {
  animation: fade-up 0.3s ease-out 0.2s backwards;
}

/* 20.5 Modal Animations (Enhanced) */
.modal-overlay.modal-opening .modal-content {
  animation: modal-open 0.3s cubic-bezier(0.34, 1.56, 0.64, 1) forwards;
}

.modal-overlay.modal-closing .modal-content {
  animation: modal-close 0.2s ease-out forwards;
}

.modal-overlay.modal-opening .modal-backdrop {
  animation: fade-in 0.3s ease forwards;
}

/* 20.6 Progress Bar Animation — CONSOLIDATED */
/* ⚡ PERFORMANCE: Canonical #progressBar styles now in Section 7 above */

.quiz-pulse {
  animation: pulse-scale 0.6s ease;
}

/* 20.7 Timer Animations */
#examTimer.low-time {
  animation: countdown-flash 1s ease infinite;
}

/* 20.8 Settings Button Animation */
#settingsBtn:hover i {
  animation: icon-rotate 0.5s ease;
}

/* 20.9 Button Hover Effects */
.btn-primary,
.btn-submit,
#submitExamButton {
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease;
  will-change: transform;
}

.btn-primary:hover,
.btn-submit:hover,
#submitExamButton:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
}

.btn-primary:active,
.btn-submit:active,
#submitExamButton:active {
  transform: translateY(0);
}

/* ========================================
   21. ACCESSIBILITY
   ======================================== */

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .quiz-pulse,
  .quiz-loading,
  .quiz-countdown-pulse,
  .blob,
  #progressBar::after {
    animation: none;
  }

  .option-card:hover {
    transform: none;
    box-shadow: none;
  }
}

/* ⚡ PERFORMANCE: Mobile optimization - giảm animations để tiết kiệm pin */
@media (max-width: 640px) {
  /* Đơn giản hóa transitions trên mobile */
  .option-card {
    transition:
      background-color 0.15s ease,
      border-color 0.15s ease,
      opacity 0.2s ease;
  }

  /* Tắt hover transforms trên mobile (touch không cần) */
  .option-card:hover {
    transform: none;
    box-shadow: none;
  }

  /* ⚡ CRITICAL: Tắt backdrop-filter trên mobile - rất nặng trên low-end */
  .glass-card {
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
    background: var(--card-bg);
  }

  .glass-modal {
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
    background: var(--modal-bg);
  }

  /* Giảm animation cho question zoom */
  .quiz-zoom-in {
    animation-duration: 0.15s;
  }

  .quiz-fade-out {
    animation-duration: 0.2s;
  }

  /* Giảm animation cho correct/wrong answers */
  .quiz-correct-answer,
  .quiz-wrong-answer {
    animation-duration: 0.3s;
  }

  /* Tắt progress shimmer trên mobile */
  #progressBar::after {
    animation: none;
  }

  /* Optimize scrolling */
  #questionContainer,
  .glass-card {
    -webkit-overflow-scrolling: touch;
  }
}

/* ⚡ PERFORMANCE: Touch devices - disable hover effects */
@media (hover: none) {
  .option-card:hover {
    transform: none;
    box-shadow: none;
    background-color: var(--option-bg);
  }

  .theme-purple .option-card:hover {
    filter: none;
    transform: none;
  }

  .btn-primary:hover,
  .btn-submit:hover,
  #submitExamButton:hover {
    transform: none;
    box-shadow: none;
  }
}

/* Focus visible */
:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

button:focus-visible,
.option-card:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ========================================
   21. PRINT STYLES
   ======================================== */

@media print {
  body * {
    display: none !important;
    visibility: hidden !important;
  }
}