* { margin: 0; padding: 0; box-sizing: border-box; }

:root {
  --bg: #f5f5f5;
  --card: #ffffff;
  --primary: #2563eb;
  --correct: #16a34a;
  --wrong: #dc2626;
  --text: #1f2937;
  --muted: #6b7280;
  --border: #e5e7eb;
  --exp-bg: #fffbeb;
  --exp-border: #fde68a;
  --exp-title: #92400e;
  --selected-bg: #eff6ff;
  --correct-bg: #f0fdf4;
  --wrong-bg: #fef2f2;
  --radius: 8px;
}

[data-theme="dark"] {
  --bg: #111827;
  --card: #1f2937;
  --primary: #3b82f6;
  --correct: #22c55e;
  --wrong: #ef4444;
  --text: #f9fafb;
  --muted: #9ca3af;
  --border: #374151;
  --exp-bg: #292524;
  --exp-border: #78716c;
  --exp-title: #fbbf24;
  --selected-bg: #1e3a8a;
  --correct-bg: #14532d;
  --wrong-bg: #7f1d1d;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  transition: background 0.2s, color 0.2s;
}

#app {
  max-width: 720px;
  margin: 0 auto;
  padding: 16px;
}

header { text-align: center; margin-bottom: 16px; }

.header-top {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
}

.header-top h1 { font-size: 1.5rem; }

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

.icon-btn {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 6px;
  width: 36px;
  height: 36px;
  cursor: pointer;
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.subtitle { color: var(--muted); font-size: 0.85rem; }

.shuffle-note {
  color: var(--exp-title);
  background: var(--exp-bg);
  border: 1px solid var(--exp-border);
  border-radius: 6px;
  font-size: 0.75rem;
  padding: 6px 10px;
  margin-top: 8px;
  line-height: 1.5;
}

#mode-nav {
  display: flex;
  gap: 8px;
  margin-bottom: 12px;
}

.mode-btn {
  flex: 1;
  padding: 10px;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--text);
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s;
}

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

#filters {
  background: var(--card);
  border-radius: var(--radius);
  padding: 12px;
  margin-bottom: 12px;
}

.filter-group {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
}

.filter-group:last-child { margin-bottom: 0; }
.filter-group label { font-size: 0.85rem; color: var(--muted); white-space: nowrap; }

.cat-btn {
  padding: 6px 14px;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--text);
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.85rem;
}

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

#section-select {
  flex: 1;
  padding: 6px 10px;
  border: 1px solid var(--border);
  border-radius: 4px;
  font-size: 0.85rem;
  background: var(--card);
  color: var(--text);
}

#progress-bar {
  position: relative;
  height: 24px;
  background: var(--border);
  border-radius: 12px;
  margin-bottom: 16px;
  overflow: hidden;
}

#progress-fill {
  height: 100%;
  background: var(--primary);
  border-radius: 12px;
  transition: width 0.3s;
  width: 0%;
}

#progress-text {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text);
}

#jump-bar {
  display: flex;
  gap: 8px;
  margin-bottom: 4px;
}

#jump-hint {
  font-size: 0.72rem;
  color: var(--muted);
  line-height: 1.6;
  margin: 0 0 12px;
}

#jump-hint code {
  background: var(--border);
  border-radius: 3px;
  padding: 1px 5px;
  font-size: 0.7rem;
}

#jump-input {
  width: 120px;
  padding: 6px 10px;
  border: 1px solid var(--border);
  border-radius: 4px;
  font-size: 0.85rem;
  background: var(--card);
  color: var(--text);
}

#jump-input.jump-error { border-color: var(--wrong); }

#btn-jump {
  padding: 6px 16px;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--card);
  color: var(--text);
  font-size: 0.85rem;
  cursor: pointer;
  transition: all 0.2s;
}

#btn-jump:hover { border-color: var(--primary); color: var(--primary); }

#jump-msg {
  align-self: center;
  font-size: 0.8rem;
  color: var(--wrong);
  line-height: 1.4;
}

#question-card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

#q-meta {
  font-size: 0.75rem;
  color: var(--muted);
  margin-bottom: 8px;
}

#q-text {
  font-size: 1rem;
  font-weight: 500;
  margin-bottom: 16px;
  white-space: pre-wrap;
}

#q-options { display: flex; flex-direction: column; gap: 10px; }

.option-btn {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 12px;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--card);
  color: var(--text);
  cursor: pointer;
  text-align: left;
  font-size: 0.9rem;
  transition: border-color 0.2s;
  width: 100%;
}

.option-btn:hover { border-color: var(--primary); }
.option-btn.selected { border-color: var(--primary); background: var(--selected-bg); }
.option-btn.correct { border-color: var(--correct); background: var(--correct-bg); }
.option-btn.wrong { border-color: var(--wrong); background: var(--wrong-bg); }
.option-btn.disabled { pointer-events: none; }

.option-letter {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--border);
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  font-weight: 600;
}

.option-btn.selected .option-letter { background: var(--primary); color: #fff; }
.option-btn.correct .option-letter { background: var(--correct); color: #fff; }
.option-btn.wrong .option-letter { background: var(--wrong); color: #fff; }

#q-answer-text {
  margin-top: 14px;
  font-size: 0.95rem;
  font-weight: 600;
}

#q-answer-text.correct-text { color: var(--correct); }
#q-answer-text.wrong-text { color: var(--wrong); }

#q-actions {
  display: flex;
  gap: 10px;
  margin-top: 16px;
}

#q-actions button {
  flex: 1;
  padding: 12px;
  border: none;
  border-radius: var(--radius);
  font-size: 0.9rem;
  cursor: pointer;
  font-weight: 500;
}

#btn-prev { background: var(--border); color: var(--text); }
#btn-prev:disabled { opacity: 0.4; cursor: not-allowed; }
#btn-confirm { background: var(--primary); color: #fff; }
#btn-next { background: var(--text); color: var(--bg); }
#btn-next-section { background: var(--primary); color: #fff; }

#q-explanation {
  margin-top: 16px;
  padding: 14px;
  background: var(--exp-bg);
  border: 1px solid var(--exp-border);
  border-radius: var(--radius);
  font-size: 0.85rem;
  line-height: 1.7;
}

#q-explanation .exp-title {
  font-weight: 600;
  margin-bottom: 6px;
  color: var(--exp-title);
}

.empty-msg {
  text-align: center;
  padding: 40px;
  color: var(--muted);
}

#exam-result {
  text-align: center;
  background: var(--card);
  border-radius: var(--radius);
  padding: 40px 20px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

#exam-result h2 { margin-bottom: 16px; }
#result-score { font-size: 2rem; font-weight: 700; margin-bottom: 8px; }
#result-pass { font-size: 1.1rem; margin-bottom: 24px; }
#result-pass.pass { color: var(--correct); }
#result-pass.fail { color: var(--wrong); }

#btn-restart {
  padding: 12px 32px;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  font-size: 1rem;
  cursor: pointer;
}

footer {
  text-align: center;
  margin-top: 16px;
  font-size: 0.8rem;
  color: var(--muted);
}

/* Modal */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 16px;
}

.modal-content {
  background: var(--card);
  color: var(--text);
  border-radius: var(--radius);
  padding: 24px;
  max-width: 480px;
  width: 100%;
  max-height: 80vh;
  overflow-y: auto;
}

.modal-content h2 { margin-bottom: 12px; }
.modal-content p { margin-bottom: 10px; font-size: 0.9rem; }
.modal-content ul { margin: 0 0 10px 20px; font-size: 0.9rem; }
.modal-content a { color: var(--primary); }

#btn-close-about {
  width: 100%;
  padding: 10px;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  font-size: 0.9rem;
  cursor: pointer;
  margin-top: 8px;
}

.hidden { display: none !important; }

@media (max-width: 480px) {
  #app { padding: 10px; }
  #question-card { padding: 14px; }
  .mode-btn { padding: 8px 4px; font-size: 0.8rem; }
}