/* ============================================
   Quiz Practice System - Responsive Styles
   Mobile-first design
   ============================================ */

/* --- CSS Variables --- */
:root {
  --color-primary: #2563eb;
  --color-primary-light: #dbeafe;
  --color-primary-dark: #1d4ed8;
  --color-success: #16a34a;
  --color-success-light: #dcfce7;
  --color-error: #dc2626;
  --color-error-light: #fef2f2;
  --color-warning: #f59e0b;
  --color-warning-light: #fffbeb;
  --color-bg: #f1f5f9;
  --color-card: #ffffff;
  --color-text: #1e293b;
  --color-text-secondary: #64748b;
  --color-text-muted: #94a3b8;
  --color-border: #e2e8f0;
  --color-border-focus: #93c5fd;
  --shadow-sm: 0 1px 2px rgba(0,0,0,.05);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,.07), 0 2px 4px -2px rgba(0,0,0,.05);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,.08), 0 4px 6px -4px rgba(0,0,0,.05);
  --radius-sm: 6px;
  --radius: 10px;
  --radius-lg: 16px;
  --transition: 0.2s ease;
  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans SC", sans-serif;
}

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

html { font-size: 16px; -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font-stack);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
}

/* --- Layout --- */
.app-container {
  max-width: 900px;
  margin: 0 auto;
  padding: 16px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* --- Header --- */
.header {
  text-align: center;
  padding: 24px 0 16px;
  flex-shrink: 0;
}

.title {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.subtitle {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin-top: 2px;
}

.header-controls {
  margin-top: 16px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

/* --- Progress Bar --- */
.progress-wrap {
  display: flex;
  align-items: center;
  gap: 10px;
}

.progress-bar {
  flex: 1;
  height: 6px;
  background: var(--color-border);
  border-radius: 3px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--color-primary);
  border-radius: 3px;
  transition: width 0.35s ease;
  width: 0%;
}

.progress-text {
  font-size: 0.8rem;
  color: var(--color-text-secondary);
  white-space: nowrap;
  min-width: 52px;
  text-align: right;
  font-variant-numeric: tabular-nums;
}

/* --- Filter Buttons --- */
.filter-group {
  display: flex;
  gap: 6px;
  justify-content: center;
  flex-wrap: wrap;
}

.filter-btn, .random-btn {
  padding: 6px 14px;
  border: 1px solid var(--color-border);
  border-radius: 20px;
  background: var(--color-card);
  color: var(--color-text-secondary);
  font-size: 0.8rem;
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
  white-space: nowrap;
}

.filter-btn:hover, .random-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.filter-btn.active {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

.random-btn.active {
  background: var(--color-warning);
  color: #fff;
  border-color: var(--color-warning);
}

/* --- Main --- */
.main {
  flex: 1;
  padding: 20px 0;
}

/* --- Question Card --- */
.question-card {
  background: var(--color-card);
  border-radius: var(--radius-lg);
  padding: 24px;
  box-shadow: var(--shadow-md);
  transition: opacity 0.25s ease, transform 0.25s ease;
}

.question-card.switching {
  opacity: 0;
  transform: translateY(8px);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
  flex-wrap: wrap;
  gap: 8px;
}

.type-badge {
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.02em;
}

.type-badge.single {
  background: var(--color-primary-light);
  color: var(--color-primary-dark);
}

.type-badge.multiple {
  background: var(--color-warning-light);
  color: #b45309;
}

.type-badge.judge {
  background: var(--color-success-light);
  color: #15803d;
}

.question-num {
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.question-stem {
  font-size: 1.1rem;
  font-weight: 600;
  line-height: 1.7;
  margin-bottom: 24px;
  color: var(--color-text);
}

.question-stem .katex { font-size: 1.05em; }

/* --- Options --- */
.options-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option-item {
  position: relative;
  display: flex;
  align-items: flex-start;
  padding: 14px 16px;
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--transition);
  background: var(--color-card);
  gap: 12px;
  -webkit-tap-highlight-color: transparent;
  user-select: none;
}

.option-item:hover {
  border-color: var(--color-border-focus);
  background: #f8fafc;
}

.option-item:active {
  transform: scale(0.99);
}

.option-item.selected {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.option-item.correct {
  border-color: var(--color-success);
  background: var(--color-success-light);
}

.option-item.incorrect {
  border-color: var(--color-error);
  background: var(--color-error-light);
}

.option-key {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-bg);
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  flex-shrink: 0;
  transition: all var(--transition);
}

.option-item.selected .option-key {
  background: var(--color-primary);
  color: #fff;
}

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

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

.option-text {
  flex: 1;
  font-size: 0.95rem;
  line-height: 1.5;
  padding-top: 4px;
}

.option-text .katex { font-size: 1em; }

.option-icon {
  display: none;
  font-size: 0.9rem;
  padding-top: 5px;
  flex-shrink: 0;
}

.option-item.correct .option-icon,
.option-item.incorrect .option-icon {
  display: block;
}

.option-item.correct .option-icon::before { content: "✓"; color: var(--color-success); }
.option-item.incorrect .option-icon::before { content: "✗"; color: var(--color-error); }

/* --- Analysis Box --- */
.analysis-box {
  margin-top: 20px;
  padding: 16px;
  background: var(--color-bg);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
}

.analysis-title {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 6px;
}

.analysis-content {
  font-size: 0.9rem;
  color: var(--color-text);
  line-height: 1.7;
}

.analysis-content .katex { font-size: 0.95em; }

/* --- Long Answer Area (short / comprehensive) --- */
.long-answer-area {
  margin-top: 8px;
}

/* --- Type badges for new types --- */
.type-badge.short {
  background: #ede9fe;
  color: #6d28d9;
}

.type-badge.comprehensive {
  background: #fce7f3;
  color: #be185d;
}

/* --- Hint Cards --- */
.hint-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  margin-bottom: 10px;
  overflow: hidden;
  transition: all var(--transition);
}

.hint-card-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 12px 14px;
  cursor: pointer;
  user-select: none;
  transition: background var(--transition);
}

.hint-card-header:hover {
  background: rgba(0,0,0,.03);
}

.hint-icon {
  font-size: 1.1rem;
  flex-shrink: 0;
}

.hint-label {
  flex: 1;
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--color-text);
}

.hint-toggle {
  font-size: 0.7rem;
  color: var(--color-text-muted);
  transition: transform 0.2s ease;
  flex-shrink: 0;
}

.hint-card.collapsed .hint-card-body {
  display: none;
}

.hint-card.collapsed .hint-toggle {
  transform: rotate(-90deg);
}

.hint-card-body {
  padding: 0 14px 14px;
}

.hint-content {
  font-size: 0.9rem;
  line-height: 1.75;
  color: var(--color-text);
  white-space: pre-line;
}

.hint-content .katex { font-size: 0.95em; }

/* Hint card color accents */
.hint-explanation { border-left: 3px solid #8b5cf6; }
.hint-example { border-left: 3px solid #f59e0b; }
.hint-memory { border-left: 3px solid #10b981; }
.hint-answer { border-left: 3px solid var(--color-primary); }

/* --- Reveal Controls --- */
.reveal-controls {
  text-align: center;
  margin: 8px 0;
}

.btn-hint {
  background: #ede9fe;
  color: #6d28d9;
  border: 2px solid #c4b5fd;
  font-size: 0.95rem;
  padding: 14px 28px;
  cursor: pointer;
  border-radius: var(--radius);
  transition: all var(--transition);
  font-family: inherit;
  font-weight: 600;
}

.btn-hint:hover {
  background: #ddd6fe;
  border-color: #8b5cf6;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-answer-reveal {
  background: #dbeafe;
  color: var(--color-primary-dark);
  border: 2px solid #93c5fd;
  font-size: 0.95rem;
  padding: 14px 28px;
  cursor: pointer;
  border-radius: var(--radius);
  transition: all var(--transition);
  font-family: inherit;
  font-weight: 600;
}

.btn-answer-reveal:hover {
  background: #bfdbfe;
  border-color: var(--color-primary);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

/* --- Self Evaluation --- */
.self-eval-area {
  text-align: center;
  margin-top: 20px;
  padding: 20px;
  background: var(--color-bg);
  border-radius: var(--radius);
  border: 1px dashed var(--color-border);
}

.self-eval-prompt {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  margin-bottom: 14px;
}

.self-eval-buttons {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
}

.btn-self-correct,
.btn-self-incorrect {
  padding: 12px 24px;
  border-radius: var(--radius);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
  border: 2px solid transparent;
}

.btn-self-correct {
  background: var(--color-success-light);
  color: #15803d;
  border-color: #86efac;
}

.btn-self-correct:hover {
  background: #bbf7d0;
  border-color: var(--color-success);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

.btn-self-incorrect {
  background: var(--color-warning-light);
  color: #b45309;
  border-color: #fcd34d;
}

.btn-self-incorrect:hover {
  background: #fef3c7;
  border-color: var(--color-warning);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

.self-eval-result {
  text-align: center;
  margin-top: 16px;
  padding: 12px;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
}

.self-eval-correct {
  background: var(--color-success-light);
  color: #15803d;
}

.self-eval-incorrect {
  background: var(--color-warning-light);
  color: #b45309;
}

/* --- Navigation --- */
.nav-bar {
  display: flex;
  justify-content: center;
  gap: 12px;
  padding: 16px 0 8px;
  flex-shrink: 0;
}

/* --- Buttons --- */
.btn {
  padding: 12px 24px;
  border: 2px solid transparent;
  border-radius: var(--radius);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
  -webkit-tap-highlight-color: transparent;
  white-space: nowrap;
}

.btn:active { transform: scale(0.97); }

.btn-primary {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

.btn-primary:hover { background: var(--color-primary-dark); }

.btn-outline {
  background: transparent;
  color: var(--color-text-secondary);
  border-color: var(--color-border);
}

.btn-outline:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.btn-accent {
  background: var(--color-success);
  color: #fff;
  border-color: var(--color-success);
}

.btn-accent:hover { background: #15803d; }

.btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
  pointer-events: none;
}

/* --- Keyboard Hint --- */
.keyboard-hint {
  text-align: center;
  font-size: 0.7rem;
  color: var(--color-text-muted);
  padding: 8px 0 16px;
  flex-shrink: 0;
}

/* --- Result Area --- */
.result-area {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 50vh;
}

.result-card {
  text-align: center;
  background: var(--color-card);
  border-radius: var(--radius-lg);
  padding: 40px 32px;
  box-shadow: var(--shadow-md);
  max-width: 480px;
  width: 100%;
}

.result-icon {
  font-size: 4rem;
  margin-bottom: 8px;
}

.result-score {
  font-size: 2.5rem;
  font-weight: 800;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

.result-detail {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  margin: 8px 0 20px;
}

.result-stats {
  display: flex;
  justify-content: center;
  gap: 24px;
  margin-bottom: 28px;
  flex-wrap: wrap;
}

.stat-item {
  text-align: center;
}

.stat-num {
  font-size: 1.5rem;
  font-weight: 700;
}

.stat-num.green { color: var(--color-success); }
.stat-num.red { color: var(--color-error); }
.stat-num.blue { color: var(--color-primary); }

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

.result-card .btn {
  margin: 6px;
}

/* --- Empty State --- */
.empty-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--color-text-muted);
}

.empty-state .icon { font-size: 3rem; margin-bottom: 12px; }
.empty-state p { font-size: 0.95rem; }

/* ============================================
   Tablet: >= 600px
   ============================================ */
@media (min-width: 600px) {
  .app-container { padding: 24px; }

  .title { font-size: 1.6rem; }

  .options-list {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .long-answer-area {
    grid-column: 1 / -1;
  }

  .nav-bar { gap: 16px; padding: 20px 0 12px; }

  .btn { padding: 12px 32px; }

  .header-controls { gap: 16px; }

  .filter-btn, .random-btn { padding: 7px 18px; font-size: 0.85rem; }
}

/* ============================================
   Desktop: >= 900px
   ============================================ */
@media (min-width: 900px) {
  .app-container { padding: 32px; }

  .title { font-size: 1.8rem; }

  .question-card { padding: 32px; }

  .question-stem { font-size: 1.2rem; }

  .option-item { padding: 16px 20px; }

  .option-text { font-size: 1rem; }

  .header-controls {
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
  }

  .progress-wrap { flex: 1; max-width: 400px; }

  .keyboard-hint { padding: 12px 0 20px; }
}

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

/* ============================================
   Dark mode (optional)
   ============================================ */
@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #0f172a;
    --color-card: #1e293b;
    --color-text: #f1f5f9;
    --color-text-secondary: #94a3b8;
    --color-text-muted: #64748b;
    --color-border: #334155;
    --color-border-focus: #3b82f6;
    --color-primary-light: #1e3a5f;
    --color-success-light: #14532d;
    --color-error-light: #450a0a;
    --color-warning-light: #451a03;
    --shadow-sm: 0 1px 2px rgba(0,0,0,.3);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,.4);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,.5);
  }

  .option-item:hover { background: #1e293b; }
  .analysis-box { background: #0f172a; }

  /* Dark mode — new components */
  .type-badge.short { background: #2e1065; color: #c4b5fd; }
  .type-badge.comprehensive { background: #500724; color: #fbcfe8; }

  .hint-card { background: #0f172a; border-color: #334155; }
  .hint-card-header:hover { background: rgba(255,255,255,.04); }
  .hint-explanation { border-left-color: #7c3aed; }
  .hint-example { border-left-color: #d97706; }
  .hint-memory { border-left-color: #059669; }
  .hint-answer { border-left-color: #3b82f6; }

  .btn-hint { background: #2e1065; color: #c4b5fd; border-color: #6d28d9; }
  .btn-hint:hover { background: #3b0764; border-color: #8b5cf6; }
  .btn-answer-reveal { background: #1e3a5f; color: #93c5fd; border-color: #3b82f6; }
  .btn-answer-reveal:hover { background: #1e3a5f; border-color: #60a5fa; }

  .self-eval-area { background: #0f172a; border-color: #334155; }
  .btn-self-correct { background: #14532d; color: #86efac; border-color: #16a34a; }
  .btn-self-correct:hover { background: #166534; }
  .btn-self-incorrect { background: #451a03; color: #fcd34d; border-color: #d97706; }
  .btn-self-incorrect:hover { background: #581c0f; }
  .self-eval-correct { background: #14532d; color: #86efac; }
  .self-eval-incorrect { background: #451a03; color: #fcd34d; }
}