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

:root {
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --success: #16a34a;
  --success-bg: #dcfce7;
  --danger: #dc2626;
  --danger-bg: #fee2e2;
  --warning: #f59e0b;
  --warning-bg: #fef3c7;
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-400: #9ca3af;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-800: #1f2937;
  --gray-900: #111827;
  --radius: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.1), 0 2px 4px rgba(0,0,0,0.06);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--gray-50);
  color: var(--gray-800);
  line-height: 1.6;
  min-height: 100vh;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 20px;
}

/* View toggling */
.view { display: none; }
.view.active { display: block; }

/* Header */
.app-header {
  text-align: center;
  padding: 30px 0 20px;
}

.app-header h1 {
  font-size: 1.8rem;
  color: var(--gray-900);
}

.app-header p {
  color: var(--gray-500);
  margin-top: 4px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 20px;
  border: none;
  border-radius: var(--radius);
  font-size: 0.95rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s;
}

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

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

.btn-secondary {
  background: var(--gray-200);
  color: var(--gray-700);
}
.btn-secondary:hover { background: var(--gray-300); }

.btn-danger {
  background: var(--danger);
  color: #fff;
}
.btn-danger:hover { background: #b91c1c; }

.btn-success {
  background: var(--success);
  color: #fff;
}
.btn-success:hover { background: #15803d; }

.btn-sm {
  padding: 6px 14px;
  font-size: 0.85rem;
}

.btn-lg {
  padding: 14px 32px;
  font-size: 1.1rem;
}

/* Cards */
.card {
  background: #fff;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 24px;
  margin-bottom: 16px;
}

/* ─── HOME VIEW ─── */
.config-section { margin-bottom: 24px; }

.config-section label {
  display: block;
  font-weight: 600;
  margin-bottom: 8px;
  color: var(--gray-700);
}

.config-section .hint {
  font-size: 0.85rem;
  color: var(--gray-400);
  margin-top: 4px;
}

.slider-row {
  display: flex;
  align-items: center;
  gap: 12px;
}

.slider-row input[type="range"] {
  flex: 1;
  accent-color: var(--primary);
}

.slider-row .slider-value {
  min-width: 48px;
  text-align: center;
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--primary);
}

.time-input {
  width: 100px;
  padding: 8px 12px;
  border: 1px solid var(--gray-300);
  border-radius: var(--radius);
  font-size: 1rem;
  text-align: center;
}

.time-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.presets {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}

.preset-btn {
  padding: 10px 18px;
  background: var(--gray-100);
  border: 2px solid var(--gray-200);
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 500;
  transition: border-color 0.15s, background 0.15s;
}

.preset-btn:hover {
  border-color: var(--primary);
  background: #eff6ff;
}

.home-actions {
  display: flex;
  gap: 12px;
  margin-top: 24px;
}

/* ─── QUIZ VIEW ─── */
.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 0;
  margin-bottom: 16px;
  border-bottom: 1px solid var(--gray-200);
  flex-wrap: wrap;
  gap: 10px;
}

.timer {
  font-size: 1.3rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: var(--gray-700);
  min-width: 70px;
}

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

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

.progress-text {
  font-weight: 600;
  color: var(--gray-600);
}

.question-card {
  background: #fff;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 28px;
  margin-bottom: 16px;
}

.question-number {
  font-size: 0.85rem;
  color: var(--gray-400);
  margin-bottom: 8px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.question-text {
  font-size: 1.15rem;
  font-weight: 600;
  line-height: 1.5;
  margin-bottom: 20px;
  color: var(--gray-900);
}

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

.option-card {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 14px 16px;
  border: 2px solid var(--gray-200);
  border-radius: var(--radius);
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}

.option-card:hover {
  border-color: var(--primary);
  background: #f0f5ff;
}

.option-card.selected {
  border-color: var(--primary);
  background: #eff6ff;
}

.option-letter {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--gray-100);
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--gray-500);
  flex-shrink: 0;
}

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

.option-text {
  padding-top: 3px;
  line-height: 1.4;
}

.quiz-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.quiz-footer .nav-btns {
  display: flex;
  gap: 8px;
}

.flag-btn { position: relative; }
.flag-btn.flagged {
  background: var(--warning);
  color: #fff;
}

/* Navigator grid */
.navigator {
  margin-top: 16px;
}

.navigator h3 {
  font-size: 0.9rem;
  color: var(--gray-500);
  margin-bottom: 10px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.nav-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.nav-cell {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  border: 2px solid transparent;
  transition: all 0.1s;
}

.nav-cell.unanswered {
  background: var(--gray-100);
  color: var(--gray-500);
}

.nav-cell.answered {
  background: #dbeafe;
  color: var(--primary);
}

.nav-cell.flagged {
  background: var(--warning-bg);
  color: #b45309;
}

.nav-cell.current {
  border-color: var(--gray-900);
}

.nav-legend {
  display: flex;
  gap: 16px;
  margin-top: 10px;
  font-size: 0.8rem;
  color: var(--gray-500);
}

.nav-legend span {
  display: flex;
  align-items: center;
  gap: 4px;
}

.legend-dot {
  width: 12px;
  height: 12px;
  border-radius: 3px;
}

.legend-dot.gray { background: var(--gray-100); }
.legend-dot.blue { background: #dbeafe; }
.legend-dot.orange { background: var(--warning-bg); }

/* ─── RESULTS VIEW ─── */
.score-display {
  text-align: center;
  padding: 32px;
}

.score-number {
  font-size: 3rem;
  font-weight: 800;
  color: var(--gray-900);
}

.score-percentage {
  font-size: 1.5rem;
  color: var(--gray-500);
  margin-left: 8px;
}

.badge {
  display: inline-block;
  padding: 6px 18px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 0.9rem;
  margin-top: 12px;
}

.badge.pass {
  background: var(--success-bg);
  color: var(--success);
}

.badge.fail {
  background: var(--danger-bg);
  color: var(--danger);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 12px;
  margin: 20px 0;
}

.stat-card {
  text-align: center;
  padding: 16px;
  background: var(--gray-50);
  border-radius: var(--radius);
}

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

.stat-card .stat-label {
  font-size: 0.8rem;
  color: var(--gray-500);
  margin-top: 2px;
}

.stat-card.correct .stat-value { color: var(--success); }
.stat-card.incorrect .stat-value { color: var(--danger); }
.stat-card.unanswered .stat-value { color: var(--warning); }

.results-actions {
  display: flex;
  gap: 12px;
  justify-content: center;
  margin: 24px 0;
}

/* Review */
.review-section h2 {
  font-size: 1.2rem;
  margin-bottom: 16px;
  color: var(--gray-700);
}

.review-item {
  background: #fff;
  border-radius: var(--radius);
  border: 1px solid var(--gray-200);
  padding: 20px;
  margin-bottom: 12px;
}

.review-item .review-q {
  font-weight: 600;
  margin-bottom: 10px;
}

.review-item .review-q-number {
  color: var(--gray-400);
  font-weight: 400;
  font-size: 0.85rem;
}

.review-option {
  padding: 8px 12px;
  border-radius: 6px;
  margin-bottom: 4px;
  font-size: 0.95rem;
  display: flex;
  align-items: flex-start;
  gap: 8px;
}

.review-option .opt-letter {
  font-weight: 700;
  min-width: 20px;
}

.review-option.correct-answer {
  background: var(--success-bg);
  color: #166534;
  font-weight: 500;
}

.review-option.wrong-pick {
  background: var(--danger-bg);
  color: #991b1b;
  font-weight: 500;
}

.review-item .review-status {
  display: inline-block;
  font-size: 0.8rem;
  font-weight: 700;
  padding: 2px 10px;
  border-radius: 999px;
  margin-bottom: 10px;
}

.review-status.correct {
  background: var(--success-bg);
  color: var(--success);
}

.review-status.incorrect {
  background: var(--danger-bg);
  color: var(--danger);
}

.review-status.skipped {
  background: var(--warning-bg);
  color: #92400e;
}

.review-explanation {
  margin-top: 12px;
  padding: 14px 16px;
  background: #eff6ff;
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius) var(--radius) 0;
}
.review-explanation-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--primary);
  margin-bottom: 6px;
}
.review-explanation p {
  margin: 0;
  font-size: 0.92rem;
  line-height: 1.55;
  color: var(--gray-700);
}

/* ─── HISTORY VIEW ─── */
.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 10px;
}

.history-header h2 {
  font-size: 1.3rem;
}

.history-empty {
  text-align: center;
  padding: 60px 20px;
  color: var(--gray-400);
}

.history-empty p {
  font-size: 1.1rem;
  margin-bottom: 16px;
}

.history-item {
  background: #fff;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 16px 20px;
  margin-bottom: 10px;
  cursor: pointer;
  transition: box-shadow 0.15s;
}

.history-item:hover { box-shadow: var(--shadow-md); }

.history-summary {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 8px;
}

.history-date {
  font-weight: 600;
  color: var(--gray-700);
}

.history-score {
  font-weight: 700;
  font-size: 1.1rem;
}

.history-meta {
  display: flex;
  gap: 16px;
  font-size: 0.85rem;
  color: var(--gray-500);
  margin-top: 4px;
}

.history-detail {
  display: none;
  margin-top: 12px;
  padding-top: 12px;
  border-top: 1px solid var(--gray-200);
}

.history-detail.open { display: block; }

.history-detail-actions {
  display: flex;
  gap: 8px;
  margin-top: 10px;
}

/* ─── MODAL ─── */
.modal-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.4);
  z-index: 1000;
  align-items: center;
  justify-content: center;
}

.modal-overlay.active {
  display: flex;
}

.modal {
  background: #fff;
  border-radius: 12px;
  padding: 28px;
  max-width: 420px;
  width: 90%;
  box-shadow: 0 20px 60px rgba(0,0,0,0.2);
}

.modal h3 {
  margin-bottom: 12px;
  font-size: 1.15rem;
}

.modal p {
  color: var(--gray-600);
  margin-bottom: 20px;
  line-height: 1.5;
}

.modal-actions {
  display: flex;
  gap: 10px;
  justify-content: flex-end;
}

/* ─── RESPONSIVE ─── */
@media (max-width: 600px) {
  .container { padding: 12px; }
  .app-header h1 { font-size: 1.4rem; }
  .question-card { padding: 18px; }
  .quiz-header { font-size: 0.9rem; }
  .timer { font-size: 1.1rem; }
  .score-number { font-size: 2.2rem; }
  .home-actions, .results-actions { flex-direction: column; }
  .btn-lg { width: 100%; }
  .presets { flex-direction: column; }
  .preset-btn { width: 100%; text-align: center; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
}