/* ===== CSS Custom Properties ===== */
:root {
  --bg-primary: #1a1a2e;
  --bg-secondary: #16213e;
  --bg-card: #0f3460;
  --text-primary: #e8e8e8;
  --text-secondary: #a8a8b8;
  --text-heading: #ffffff;
  --accent-red: #FF6B6B;
  --accent-teal: #4ECDC4;
  --accent-yellow: #FFE66D;
  --accent-purple: #A06CD5;
  --accent-orange: #FF8C42;
  --accent-cyan: #2EC4B6;
  --accent-pink: #FF6B9D;
  --correct: #00C851;
  --incorrect: #ff4444;
  --gold: #FFD700;
  --silver: #C0C0C0;
  --bronze: #CD7F32;
  --font-display: 'Bangers', cursive;
  --font-body: 'Nunito', sans-serif;
  --radius: 16px;
  --radius-sm: 8px;
  --shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 16px 48px rgba(0, 0, 0, 0.4);
  --transition: 0.3s ease;
}

/* ===== Reset & Base ===== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 22px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  overflow-x: hidden;
}

/* ===== Navigation ===== */
#nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.75rem 2rem;
  background: var(--bg-secondary);
  border-bottom: 2px solid rgba(255, 255, 255, 0.1);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-brand {
  text-decoration: none;
  display: flex;
  align-items: center;
}

.nav-logo {
  height: 42px;
  width: 168px;
}

.nav-links {
  display: flex;
  gap: 1.5rem;
}

.nav-links a {
  color: var(--text-secondary);
  text-decoration: none;
  font-weight: 700;
  font-size: 1.05rem;
  transition: color var(--transition);
}

.nav-links a:hover {
  color: var(--text-heading);
}

/* ===== Main App Container ===== */
#app {
  max-width: 1000px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
  min-height: calc(100vh - 60px);
}

/* ===== Screen Titles ===== */
.screen-title {
  font-family: var(--font-display);
  font-size: 2.8rem;
  text-align: center;
  letter-spacing: 1px;
  margin-bottom: 0.5rem;
  color: var(--text-heading);
}

.screen-subtitle {
  text-align: center;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  font-size: 1.25rem;
}

/* ===== Home Screen ===== */
.home-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 70vh;
  gap: 1.5rem;
}

.home-title {
  font-family: var(--font-display);
  font-size: 4.5rem;
  text-align: center;
  letter-spacing: 2px;
  text-transform: uppercase;
  background: linear-gradient(135deg, var(--accent-yellow), var(--accent-orange), var(--accent-red));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 0.25rem;
}

.home-tagline {
  font-size: 1.35rem;
  color: var(--text-secondary);
  margin-bottom: 1.5rem;
  text-align: center;
}

.home-buttons {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  width: 100%;
  max-width: 400px;
}

.home-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  padding: 1.25rem 2rem;
  border: none;
  border-radius: var(--radius);
  font-family: var(--font-display);
  font-size: 1.5rem;
  color: #fff;
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition);
  box-shadow: var(--shadow);
  text-decoration: none;
  min-height: 80px;
}

.home-btn:hover {
  transform: translateY(-4px) scale(1.02);
  box-shadow: var(--shadow-lg);
}

.home-btn:active {
  transform: translateY(0) scale(0.98);
}

.home-btn--flashcards {
  background: linear-gradient(135deg, var(--accent-teal), #38a89d);
}

.home-btn--quiz {
  background: linear-gradient(135deg, var(--accent-orange), var(--accent-red));
}

.home-btn--leaderboard {
  background: linear-gradient(135deg, var(--accent-purple), #7c4dff);
}

.home-btn-emoji {
  font-size: 2rem;
}

/* ===== Book Select Grid ===== */
.book-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.25rem;
  margin-top: 1rem;
}

.book-card {
  padding: 1.5rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition);
  box-shadow: var(--shadow);
  text-align: center;
  border: 2px solid transparent;
  position: relative;
  overflow: hidden;
}

.book-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.15);
  border-radius: var(--radius);
}

.book-card > * {
  position: relative;
  z-index: 1;
}

.book-card:hover {
  transform: translateY(-6px) scale(1.03);
  box-shadow: var(--shadow-lg);
  border-color: rgba(255, 255, 255, 0.3);
}

.book-card-emoji {
  font-size: 3rem;
  margin-bottom: 0.5rem;
  display: block;
}

.book-card-title {
  font-family: var(--font-display);
  font-size: 1.3rem;
  color: #fff;
  margin-bottom: 0.25rem;
}

.book-card-author {
  font-size: 0.95rem;
  color: rgba(255, 255, 255, 0.75);
}

.book-card--all {
  background: linear-gradient(135deg, #FF6B6B, #4ECDC4, #FFE66D, #A06CD5, #FF8C42, #2EC4B6) !important;
  border: 2px solid rgba(255, 255, 255, 0.3);
}

/* ===== Flashcard Screen ===== */
.flashcard-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
}

.flashcard-wrapper {
  perspective: 1200px;
  width: 100%;
  max-width: 600px;
  height: 360px;
  cursor: pointer;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  transform-style: preserve-3d;
}

.flashcard-inner.flipped {
  transform: rotateY(180deg);
}

.flashcard-face {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 2rem;
  text-align: center;
  font-size: 1.4rem;
  line-height: 1.6;
  box-shadow: var(--shadow);
}

.flashcard-front {
  background: var(--bg-card);
  border: 2px solid var(--accent-teal);
  color: var(--text-heading);
  font-weight: 700;
}

.flashcard-back {
  background: linear-gradient(135deg, var(--bg-card), var(--bg-secondary));
  border: 2px solid var(--accent-yellow);
  color: var(--accent-yellow);
  transform: rotateY(180deg);
}

.flashcard-hint {
  font-size: 0.85rem;
  color: var(--text-secondary);
  text-align: center;
}

.flashcard-controls {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.flashcard-nav-btn {
  background: var(--bg-card);
  border: 2px solid rgba(255, 255, 255, 0.15);
  color: var(--text-primary);
  width: 50px;
  height: 50px;
  border-radius: 50%;
  font-size: 1.3rem;
  cursor: pointer;
  transition: all var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.flashcard-nav-btn:hover {
  background: var(--bg-secondary);
  border-color: var(--accent-teal);
  color: var(--accent-teal);
}

.flashcard-counter {
  font-family: var(--font-body);
  font-size: 1.1rem;
  color: var(--text-secondary);
  min-width: 60px;
  text-align: center;
}

.shuffle-btn {
  background: var(--bg-card);
  border: 2px solid var(--accent-purple);
  color: var(--accent-purple);
  padding: 0.6rem 1.5rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all var(--transition);
}

.shuffle-btn:hover {
  background: var(--accent-purple);
  color: #fff;
}

/* ===== Quiz Screen ===== */
.quiz-container {
  max-width: 650px;
  margin: 0 auto;
}

.quiz-name-form {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  margin-top: 2rem;
}

.quiz-name-input {
  background: var(--bg-card);
  border: 2px solid var(--accent-orange);
  border-radius: var(--radius-sm);
  color: var(--text-heading);
  font-family: var(--font-body);
  font-size: 1.2rem;
  padding: 0.75rem 1.25rem;
  width: 100%;
  max-width: 350px;
  text-align: center;
  outline: none;
  transition: border-color var(--transition);
}

.quiz-name-input:focus {
  border-color: var(--accent-yellow);
}

.quiz-name-input::placeholder {
  color: var(--text-secondary);
}

.quiz-start-btn {
  background: linear-gradient(135deg, var(--accent-orange), var(--accent-red));
  border: none;
  color: #fff;
  font-family: var(--font-display);
  font-size: 1.2rem;
  padding: 0.75rem 2.5rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition);
  box-shadow: var(--shadow);
}

.quiz-start-btn:hover {
  transform: scale(1.05);
  box-shadow: var(--shadow-lg);
}

.quiz-start-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

.quiz-question-text {
  font-family: var(--font-display);
  font-size: 1.5rem;
  color: var(--text-heading);
  text-align: center;
  margin-bottom: 1.5rem;
  line-height: 1.4;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  padding: 1rem 1.25rem;
  background: var(--bg-card);
  border: 2px solid rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 1.15rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  text-align: left;
}

.quiz-option:hover:not(.quiz-option--answered) {
  border-color: var(--accent-orange);
  background: rgba(255, 140, 66, 0.1);
  transform: translateX(4px);
}

.quiz-option-key {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.1);
  font-family: var(--font-display);
  font-size: 0.9rem;
  color: var(--text-secondary);
  flex-shrink: 0;
  margin-top: 0.1rem;
}

.quiz-option--correct {
  border-color: var(--correct);
  background: rgba(0, 200, 81, 0.15);
}

.quiz-option--correct .quiz-option-key {
  background: var(--correct);
  color: #fff;
}

.quiz-option--incorrect {
  border-color: var(--incorrect);
  background: rgba(255, 68, 68, 0.15);
}

.quiz-option--incorrect .quiz-option-key {
  background: var(--incorrect);
  color: #fff;
}

.quiz-option--answered {
  cursor: default;
  pointer-events: none;
}

.quiz-explanation {
  margin-top: 1rem;
  padding: 1rem;
  background: rgba(255, 255, 255, 0.05);
  border-radius: var(--radius-sm);
  border-left: 4px solid var(--accent-yellow);
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.5;
}

.quiz-next-btn {
  display: block;
  margin: 1.5rem auto 0;
  background: linear-gradient(135deg, var(--accent-teal), #38a89d);
  border: none;
  color: #fff;
  font-family: var(--font-display);
  font-size: 1.1rem;
  padding: 0.7rem 2rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: transform var(--transition);
}

.quiz-next-btn:hover {
  transform: scale(1.05);
}

/* ===== Results Screen ===== */
.results-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 60vh;
  text-align: center;
  gap: 1rem;
}

.results-score {
  font-family: var(--font-display);
  font-size: 4rem;
  color: var(--accent-yellow);
  margin: 0.5rem 0;
}

.results-stars {
  font-size: 2.5rem;
  margin: 0.5rem 0;
}

.results-message {
  font-size: 1.4rem;
  color: var(--text-secondary);
  max-width: 450px;
  line-height: 1.5;
}

.results-buttons {
  display: flex;
  gap: 1rem;
  margin-top: 1rem;
  flex-wrap: wrap;
  justify-content: center;
}

.results-btn {
  padding: 0.75rem 1.75rem;
  border: none;
  border-radius: var(--radius);
  font-family: var(--font-display);
  font-size: 1rem;
  color: #fff;
  cursor: pointer;
  transition: transform var(--transition);
  text-decoration: none;
}

.results-btn:hover {
  transform: scale(1.05);
}

.results-btn--primary {
  background: linear-gradient(135deg, var(--accent-orange), var(--accent-red));
}

.results-btn--secondary {
  background: linear-gradient(135deg, var(--accent-purple), #7c4dff);
}

.results-btn--tertiary {
  background: linear-gradient(135deg, var(--accent-teal), #38a89d);
}

/* ===== Leaderboard Screen ===== */
.leaderboard-container {
  max-width: 700px;
  margin: 0 auto;
}

.leaderboard-filters {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  justify-content: center;
  margin-bottom: 1.5rem;
}

.leaderboard-filter {
  padding: 0.5rem 1rem;
  border: 2px solid rgba(255, 255, 255, 0.15);
  border-radius: 20px;
  background: transparent;
  color: var(--text-secondary);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.85rem;
  cursor: pointer;
  transition: all var(--transition);
}

.leaderboard-filter:hover {
  border-color: rgba(255, 255, 255, 0.3);
  color: var(--text-primary);
}

.leaderboard-filter--active {
  background: var(--accent-purple);
  border-color: var(--accent-purple);
  color: #fff;
}

.leaderboard-table {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0 0.5rem;
}

.leaderboard-row {
  background: var(--bg-card);
  border-radius: var(--radius-sm);
}

.leaderboard-row td {
  padding: 0.85rem 1rem;
}

.leaderboard-row td:first-child {
  border-radius: var(--radius-sm) 0 0 var(--radius-sm);
  width: 60px;
  text-align: center;
}

.leaderboard-row td:last-child {
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  text-align: right;
}

.leaderboard-rank {
  font-family: var(--font-display);
  font-size: 1.2rem;
}

.leaderboard-rank--1 { color: var(--gold); }
.leaderboard-rank--2 { color: var(--silver); }
.leaderboard-rank--3 { color: var(--bronze); }

.leaderboard-name {
  font-weight: 700;
  color: var(--text-heading);
}

.leaderboard-book {
  font-size: 0.8rem;
  color: var(--text-secondary);
}

.leaderboard-score {
  font-family: var(--font-display);
  font-size: 1.1rem;
  color: var(--accent-yellow);
}

.leaderboard-percentage {
  font-size: 0.8rem;
  color: var(--text-secondary);
}

.leaderboard-date {
  font-size: 0.8rem;
  color: var(--text-secondary);
  white-space: nowrap;
}

.leaderboard-empty {
  text-align: center;
  color: var(--text-secondary);
  padding: 3rem;
  font-size: 1.1rem;
}

/* ===== Progress Bar ===== */
.progress-container {
  width: 100%;
  margin-bottom: 1.5rem;
}

.progress-bar-wrapper {
  width: 100%;
  height: 12px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 6px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  border-radius: 6px;
  transition: width 0.4s ease;
  background: linear-gradient(90deg, var(--accent-teal), var(--accent-yellow));
}

.progress-text {
  display: flex;
  justify-content: space-between;
  margin-top: 0.4rem;
  font-size: 0.85rem;
  color: var(--text-secondary);
  font-weight: 600;
}

/* ===== Back Button ===== */
.back-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: none;
  border: none;
  color: var(--text-secondary);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  margin-bottom: 1.5rem;
  transition: color var(--transition);
  padding: 0.25rem;
}

.back-btn:hover {
  color: var(--text-heading);
}

/* ===== Context Book Label ===== */
.context-book-label {
  text-align: center;
  color: var(--text-secondary);
  font-size: 0.85rem;
  font-weight: 700;
  margin-top: 1.25rem;
  opacity: 0.7;
}

/* ===== Footer ===== */
#site-footer {
  text-align: center;
  padding: 1.5rem 1rem;
  color: var(--text-secondary);
  font-size: 0.8rem;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}

/* ===== Confetti Canvas ===== */
#confetti-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 200;
}

/* ===== TV Mode ===== */
body.tv-mode #nav,
body.tv-mode #site-footer {
  display: none;
}

body.tv-mode #app {
  max-width: 100%;
  padding: 2rem 3rem;
}

body.tv-mode .screen-title {
  font-size: 3.5rem;
}

body.tv-mode .screen-subtitle {
  font-size: 1.4rem;
}

body.tv-mode .leaderboard-row td {
  padding: 1.1rem 1.5rem;
  font-size: 1.3rem;
}

body.tv-mode .leaderboard-rank {
  font-size: 1.8rem;
}

body.tv-mode .leaderboard-name {
  font-size: 1.4rem;
}

body.tv-mode .leaderboard-score {
  font-size: 1.5rem;
}

body.tv-mode .leaderboard-date {
  font-size: 1.1rem;
}

body.tv-mode .leaderboard-filter {
  font-size: 1.1rem;
  padding: 0.6rem 1.3rem;
}

body.tv-mode .leaderboard-container {
  max-width: 900px;
}

/* ===== Responsive ===== */
@media (max-width: 600px) {
  html {
    font-size: 18px;
  }

  #nav {
    padding: 0.5rem 1rem;
    flex-direction: column;
    gap: 0.5rem;
  }

  .nav-links {
    gap: 1rem;
  }

  #app {
    padding: 1.25rem 1rem;
  }

  .home-title {
    font-size: 2.8rem;
  }

  .book-grid {
    grid-template-columns: 1fr 1fr;
    gap: 0.75rem;
  }

  .flashcard-wrapper {
    height: 260px;
  }

  .flashcard-face {
    font-size: 1.05rem;
    padding: 1.25rem;
  }

  .results-score {
    font-size: 3rem;
  }
}