/* ========== Flashcard ========== */
.flashcard-container {
  perspective: 1200px;
  width: 100%;
  max-width: 480px;
  height: 320px;
  margin: 0 auto;
  cursor: pointer;
}

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

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

.flashcard-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: var(--radius-lg);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 32px;
  box-shadow: var(--shadow-lg);
}

.flashcard-front {
  background: linear-gradient(135deg, #667EEA 0%, #764BA2 100%);
  color: #fff;
}

.flashcard-back {
  background: var(--bg-card);
  color: var(--color-text);
  border: 2px solid var(--color-border);
  transform: rotateY(180deg);
}

.flashcard-word {
  font-size: 2.5rem;
  font-weight: 700;
  font-family: Georgia, "Times New Roman", serif;
  letter-spacing: -0.5px;
  margin-bottom: 8px;
}

.flashcard-phonetic {
  font-size: var(--fs-lg);
  opacity: 0.85;
  margin-bottom: 20px;
}

.flashcard-speak-btn {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.2);
  color: #fff;
  font-size: 1.3rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition-fast);
  backdrop-filter: blur(4px);
}

.flashcard-speak-btn:hover {
  background: rgba(255, 255, 255, 0.35);
}

.flashcard-back .flashcard-word {
  color: var(--color-text);
  font-size: 1.8rem;
}

.flashcard-back .flashcard-meaning {
  font-size: var(--fs-xl);
  color: var(--color-primary);
  font-weight: 600;
  margin-bottom: 8px;
}

.flashcard-back .flashcard-pos {
  font-size: var(--fs-sm);
  color: var(--color-text-muted);
  margin-bottom: 12px;
}

.flashcard-back .flashcard-example {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  text-align: center;
  font-style: italic;
}

.flashcard-actions {
  display: flex;
  justify-content: center;
  gap: 16px;
  margin-top: 24px;
}

.flashcard-know-btn, .flashcard-dunno-btn {
  padding: 12px 32px;
  border-radius: var(--radius-md);
  font-size: var(--fs-base);
  font-weight: 600;
  transition: all var(--transition-fast);
}

.flashcard-know-btn {
  background: var(--color-success);
  color: #fff;
}

.flashcard-know-btn:hover {
  background: #389E0D;
  transform: scale(1.05);
}

.flashcard-dunno-btn {
  background: var(--color-danger);
  color: #fff;
}

.flashcard-dunno-btn:hover {
  background: #CF1322;
  transform: scale(1.05);
}

/* ========== Quiz ========== */
.quiz-container {
  max-width: 700px;
  margin: 0 auto;
}

.quiz-progress {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 24px;
}

.quiz-progress .progress-bar {
  flex: 1;
}

.quiz-question {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 28px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
  margin-bottom: 16px;
}

.quiz-question .q-prompt {
  font-size: var(--fs-xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: 20px;
}

.quiz-question .q-word {
  font-family: Georgia, "Times New Roman", serif;
  font-size: var(--fs-3xl);
  color: var(--color-primary);
  font-weight: 700;
  text-align: center;
  margin-bottom: 24px;
  cursor: pointer;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.quiz-option {
  padding: 14px 18px;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--fs-base);
  color: var(--color-text);
  background: var(--bg-card);
  transition: all var(--transition-fast);
  cursor: pointer;
  text-align: left;
}

.quiz-option:hover {
  border-color: var(--color-primary-light);
  background: var(--color-primary-bg);
}

.quiz-option.selected {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
}

.quiz-option.correct {
  border-color: var(--color-success);
  background: var(--color-success-bg);
}

.quiz-option.wrong {
  border-color: var(--color-danger);
  background: var(--color-danger-bg);
}

.quiz-input {
  width: 100%;
  padding: 16px;
  font-size: var(--fs-xl);
  text-align: center;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--bg-card);
  color: var(--color-text);
  transition: border-color var(--transition-fast);
}

.quiz-input:focus {
  border-color: var(--color-primary);
}

.quiz-feedback {
  text-align: center;
  padding: 16px;
  margin-top: 12px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  animation: fadeIn 0.3s ease;
}

.quiz-feedback.correct {
  background: var(--color-success-bg);
  color: #389E0D;
}

.quiz-feedback.wrong {
  background: var(--color-danger-bg);
  color: #CF1322;
}

.quiz-result {
  text-align: center;
  padding: 40px;
  background: var(--bg-card);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
}

.quiz-result .score {
  font-size: 4rem;
  font-weight: 800;
  color: var(--color-primary);
}

/* ========== Word List Table ========== */
.word-table {
  width: 100%;
  border-collapse: collapse;
}

.word-table th {
  padding: 12px 16px;
  text-align: left;
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  border-bottom: 2px solid var(--color-border);
  cursor: pointer;
  user-select: none;
}

.word-table th:hover {
  color: var(--color-text);
}

.word-table th .sort-arrow {
  margin-left: 4px;
  font-size: 10px;
}

.word-table td {
  padding: 12px 16px;
  font-size: var(--fs-sm);
  color: var(--color-text);
  border-bottom: 1px solid var(--color-border-light);
}

.word-table tr:hover td {
  background: var(--bg-hover);
}

.word-table .word-en {
  font-weight: 600;
  font-family: Georgia, "Times New Roman", serif;
  color: var(--color-primary);
}

.word-table .word-status {
  display: inline-flex;
  align-items: center;
}

.word-table .status-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  margin-right: 6px;
}

.status-dot.mastered { background: var(--color-success); }
.status-dot.learning { background: var(--color-warning); }
.status-dot.new { background: var(--color-border); }

/* ========== Grade Cards ========== */
.grade-card {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
  padding: 24px;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: center;
}

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

.grade-card .grade-icon {
  font-size: 2.5rem;
  margin-bottom: 12px;
}

.grade-card h3 {
  font-size: var(--fs-lg);
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: 4px;
}

.grade-card .grade-subtitle {
  font-size: var(--fs-xs);
  color: var(--color-text-muted);
  margin-bottom: 12px;
}

.grade-card .grade-stats {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
}

/* ========== Grammar Tree ========== */
.grammar-category {
  margin-bottom: 8px;
}

.grammar-category-header {
  padding: 12px 16px;
  display: flex;
  align-items: center;
  gap: 10px;
  cursor: pointer;
  border-radius: var(--radius-sm);
  font-weight: 600;
  color: var(--color-text);
  transition: background var(--transition-fast);
}

.grammar-category-header:hover {
  background: var(--bg-hover);
}

.grammar-category-header .expand-icon {
  font-size: 10px;
  transition: transform var(--transition-fast);
  color: var(--color-text-muted);
}

.grammar-category.open .expand-icon {
  transform: rotate(90deg);
}

.grammar-items {
  padding-left: 28px;
  display: none;
}

.grammar-category.open .grammar-items {
  display: block;
}

.grammar-item {
  padding: 10px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background var(--transition-fast);
  color: var(--color-text-secondary);
  font-size: var(--fs-sm);
}

.grammar-item:hover {
  background: var(--color-primary-bg);
  color: var(--color-primary-dark);
}

/* ========== Reading Page ========== */
.reading-layout {
  display: grid;
  grid-template-columns: 1fr 380px;
  gap: 24px;
  align-items: start;
}

.reading-passage {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 32px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
  line-height: 1.9;
  font-size: var(--fs-base);
  color: var(--color-text);
}

.reading-questions {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 24px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
  position: sticky;
  top: 24px;
}

.reading-word-popup {
  position: fixed;
  background: var(--bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  padding: 14px 18px;
  z-index: 300;
  font-size: var(--fs-sm);
  max-width: 260px;
  pointer-events: none;
}

.reading-word-popup .popup-en {
  font-weight: 700;
  color: var(--color-primary);
  font-family: Georgia, serif;
}

.reading-word-popup .popup-zh {
  color: var(--color-text);
  margin-top: 4px;
}

/* ========== Exam Timer ========== */
.exam-timer {
  position: fixed;
  top: 16px;
  right: 24px;
  background: var(--bg-card);
  border: 2px solid var(--color-primary);
  border-radius: var(--radius-md);
  padding: 8px 16px;
  font-size: var(--fs-lg);
  font-weight: 700;
  color: var(--color-primary);
  font-variant-numeric: tabular-nums;
  box-shadow: var(--shadow-md);
  z-index: 150;
}

.exam-timer.warning {
  border-color: var(--color-warning);
  color: var(--color-warning);
  animation: pulse 1s infinite;
}

.exam-timer.danger {
  border-color: var(--color-danger);
  color: var(--color-danger);
  animation: pulse 0.5s infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.6; }
}

/* ========== Stats Dashboard ========== */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px;
}

.stat-card {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 24px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
  text-align: center;
}

.stat-card .stat-value {
  font-size: var(--fs-3xl);
  font-weight: 800;
  color: var(--color-primary);
}

.stat-card .stat-label {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  margin-top: 4px;
}

/* ========== Toast ========== */
.toast {
  position: fixed;
  top: 24px;
  right: 24px;
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 14px 20px;
  box-shadow: var(--shadow-lg);
  border-left: 4px solid var(--color-primary);
  font-size: var(--fs-sm);
  font-weight: 500;
  z-index: 1000;
  animation: slideInRight 0.3s ease, fadeOut 0.3s ease 2.7s forwards;
}

.toast.success { border-left-color: var(--color-success); }
.toast.error { border-left-color: var(--color-danger); }

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

@keyframes fadeOut {
  from { opacity: 1; }
  to { opacity: 0; }
}

/* ========== Modal ========== */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 500;
  animation: fadeIn 0.2s ease;
}

.modal {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  padding: 32px;
  max-width: 500px;
  width: 90%;
  box-shadow: var(--shadow-lg);
}

.modal h2 {
  font-size: var(--fs-xl);
  font-weight: 700;
  margin-bottom: 16px;
  color: var(--color-text);
}

.modal p {
  color: var(--color-text-secondary);
  margin-bottom: 24px;
}

@media (max-width: 768px) {
  .reading-layout {
    grid-template-columns: 1fr;
  }

  .reading-questions {
    position: static;
  }

  .flashcard-container {
    max-width: 100%;
    height: 260px;
  }

  .flashcard-word {
    font-size: 1.8rem;
  }

  .stats-grid {
    grid-template-columns: 1fr;
  }
}