/* ═══════════════════════════════════════════════════════════════
   Formula Sheet Memoriser — Styles
   Colourful educational aesthetic with dark mode support
   ═══════════════════════════════════════════════════════════════ */

/* ── Reset & Base ── */

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

:root {
  --bg-primary: #ffffff;
  --bg-secondary: #f0f5fa;
  --bg-tertiary: #dce6f0;
  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #4e6280;
  --border-color: #b1cde5;
  --accent: #05345C;
  --accent-hover: #042a4a;
  --accent-light: rgba(5, 52, 92, 0.08);
  --accent-glow: rgba(5, 52, 92, 0.2);
  --correct-color: #047857;
  --correct-bg: rgba(5, 150, 105, 0.12);
  --incorrect-color: #dc2626;
  --incorrect-bg: rgba(220, 38, 38, 0.12);
  --mastered-color: #047857;
  --reviewing-color: #b45309;
  --learning-color: #05345C;
  --not-started-color: #cbd5e1;
  --blank-bg: rgb(220, 230, 240);
  --blank-border: #8babc5;
  --popup-shadow: 0 8px 32px rgba(5, 52, 92, 0.12), 0 2px 8px rgba(0, 0, 0, 0.08);
  --panel-shadow: -4px 0 24px rgba(5, 52, 92, 0.1);
  --transition: 0.2s ease;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', monospace;
  --gradient-topbar: linear-gradient(135deg, #05345C 0%, #0a4a7a 50%, #1a6aaa 100%);
  --gradient-accent: linear-gradient(135deg, #05345C, #0a4a7a);
}

body {
  font-family: var(--font-sans);
  background: var(--bg-secondary);
  color: var(--text-primary);
  line-height: 1.5;
  overflow-x: hidden;
}

/* ── Dark Mode ── */

body.dark-mode {
  --bg-primary: #0b1929;
  --bg-secondary: #0f2236;
  --bg-tertiary: #163050;
  --text-primary: #e2e8f0;
  --text-secondary: #B1CDE5;
  --text-muted: #7a9bba;
  --border-color: #1e3d5c;
  --accent: #B1CDE5;
  --accent-hover: #d0e2f2;
  --accent-light: rgba(177, 205, 229, 0.1);
  --accent-glow: rgba(177, 205, 229, 0.25);
  --blank-bg: rgb(22, 48, 80);
  --blank-border: #3a6a96;
  --popup-shadow: 0 8px 32px rgba(0, 0, 0, 0.5), 0 0 0 1px rgba(177, 205, 229, 0.15);
  --panel-shadow: -4px 0 24px rgba(0, 0, 0, 0.4);
  --gradient-topbar: linear-gradient(135deg, #0b1929 0%, #0f2a45 50%, #163050 100%);
  --gradient-accent: linear-gradient(135deg, #B1CDE5, #7aa3c5);
  --mastered-color: #34d399;
  --reviewing-color: #fbbf24;
  --learning-color: #B1CDE5;
  --correct-color: #34d399;
  --correct-bg: rgba(52, 211, 153, 0.15);
  --incorrect-color: #f87171;
  --incorrect-bg: rgba(248, 113, 113, 0.15);
}

body.dark-mode .pdf-canvas {
  filter: invert(0.88) hue-rotate(180deg);
}

body.dark-mode .formula-overlay.blanked {
  background: var(--blank-bg);
  border-color: var(--blank-border);
}

/* ── Top Navigation Bar ── */

.top-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 20px;
  background: var(--gradient-topbar);
  border-bottom: none;
  position: sticky;
  top: 0;
  z-index: 100;
  height: 52px;
  box-shadow: 0 2px 12px rgba(5, 52, 92, 0.2);
}

.top-bar-left {
  display: flex;
  align-items: center;
  gap: 8px;
}

.app-title {
  font-size: 14px;
  font-weight: 700;
  color: #ffffff;
  margin-right: 16px;
  white-space: nowrap;
  letter-spacing: 0.3px;
}

.mode-buttons {
  display: flex;
  gap: 2px;
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(4px);
  border-radius: 8px;
  padding: 3px;
}

.mode-btn {
  padding: 5px 14px;
  border: none;
  background: transparent;
  color: rgba(255, 255, 255, 0.7);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  border-radius: 6px;
  transition: all var(--transition);
  white-space: nowrap;
}

.mode-btn:hover {
  color: #ffffff;
  background: rgba(255, 255, 255, 0.15);
}

.mode-btn.active {
  background: #ffffff;
  color: var(--accent);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  font-weight: 600;
}

.top-bar-center {
  display: flex;
  align-items: center;
  gap: 8px;
}

.page-buttons {
  display: flex;
  gap: 2px;
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(4px);
  border-radius: 8px;
  padding: 3px;
}

.page-btn {
  padding: 5px 14px;
  border: none;
  background: transparent;
  color: rgba(255, 255, 255, 0.7);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  border-radius: 6px;
  transition: all var(--transition);
}

.page-btn:hover {
  color: #ffffff;
  background: rgba(255, 255, 255, 0.15);
}

.page-btn.active {
  background: #ffffff;
  color: var(--accent);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  font-weight: 600;
}

.top-bar-right {
  display: flex;
  align-items: center;
  gap: 8px;
}

.icon-btn {
  width: 34px;
  height: 34px;
  border: none;
  background: rgba(255, 255, 255, 0.1);
  color: rgba(255, 255, 255, 0.8);
  cursor: pointer;
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  transition: all var(--transition);
}

.icon-btn:hover {
  background: rgba(255, 255, 255, 0.25);
  color: #ffffff;
}

/* ── Session Banner ── */

.session-banner {
  display: none;
  align-items: center;
  justify-content: center;
  gap: 12px;
  padding: 10px 20px;
  background: linear-gradient(90deg, #edf3f9, #f0f5fa);
  border-bottom: 1px solid var(--border-color);
  font-size: 14px;
  color: #05345C;
  font-weight: 500;
}

body.dark-mode .session-banner {
  background: linear-gradient(90deg, #0f2236, #163050);
  border-color: var(--border-color);
  color: #B1CDE5;
}

.btn-close-banner {
  background: none;
  border: none;
  font-size: 18px;
  cursor: pointer;
  color: inherit;
  opacity: 0.6;
}

.btn-close-banner:hover {
  opacity: 1;
}

/* ── Practice Controls ── */

.practice-controls {
  display: none;
  align-items: center;
  justify-content: center;
  gap: 16px;
  padding: 10px 20px;
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  font-size: 13px;
}

.practice-info {
  color: var(--text-secondary);
  display: flex;
  gap: 16px;
}

.practice-info.active {
  color: var(--accent);
  font-weight: 600;
}

/* ── Session Progress ── */

.session-progress {
  display: none;
  align-items: center;
  justify-content: center;
  gap: 12px;
  padding: 6px 20px;
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  font-size: 13px;
}

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

.progress-correct {
  color: var(--correct-color);
  font-weight: 500;
}

.progress-incorrect {
  color: var(--incorrect-color);
  font-weight: 500;
}

.progress-bar-mini {
  width: 120px;
  height: 4px;
  background: var(--bg-tertiary);
  border-radius: 2px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background: var(--gradient-accent);
  border-radius: 2px;
  transition: width 0.3s ease;
}

/* ── Main Sheet Container ── */

#sheet-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 20px;
  min-height: calc(100vh - 48px);
}

.page-wrapper {
  display: flex;
  justify-content: center;
}

.canvas-container {
  position: relative;
  display: inline-block;
  box-shadow: 0 4px 20px rgba(5, 52, 92, 0.1), 0 1px 6px rgba(0, 0, 0, 0.08);
  background: white;
  border-radius: 8px;
  overflow: hidden;
}

body.dark-mode .canvas-container {
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4), 0 0 0 1px rgba(177, 205, 229, 0.15);
}

.pdf-canvas {
  display: block;
}

.overlay-layer {
  position: absolute;
  top: 0;
  left: 0;
  pointer-events: none;
}

/* ── Formula Overlays ── */

.formula-overlay {
  position: absolute;
  pointer-events: auto;
  border-radius: 2px;
  transition: all 0.15s ease;
}

/* Study mode overlay — transparent, clickable */
.formula-overlay.study-overlay {
  cursor: pointer;
  border: 1.5px solid transparent;
}

.formula-overlay.study-overlay:hover,
.formula-overlay.study-hover {
  border-color: rgba(5, 52, 92, 0.3);
  background: rgba(5, 52, 92, 0.05);
}

/* Blanked overlay */
.formula-overlay.blanked {
  background: var(--blank-bg);
  border: 2px dashed var(--blank-border);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}

.formula-overlay.blanked:hover {
  border-color: var(--accent);
  background: rgb(200, 218, 235);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

body.dark-mode .formula-overlay.blanked:hover {
  background: rgb(30, 61, 92);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

/* Revealed states */
.formula-overlay.revealed.correct {
  background: var(--correct-bg);
  border: 2px solid var(--correct-color);
  pointer-events: none;
}

.formula-overlay.revealed.incorrect {
  background: var(--incorrect-bg);
  border: 2px solid var(--incorrect-color);
}

/* Mastery overlay colours */
.formula-overlay.mastery-mastered {
  background: rgba(22, 163, 74, 0.12);
  border: 1.5px solid rgba(22, 163, 74, 0.3);
}

.formula-overlay.mastery-reviewing {
  background: rgba(245, 158, 11, 0.12);
  border: 1.5px solid rgba(245, 158, 11, 0.3);
}

.formula-overlay.mastery-learning {
  background: rgba(59, 130, 246, 0.12);
  border: 1.5px solid rgba(59, 130, 246, 0.3);
}

/* Reconstruction mode numbering */
.reconstruct-number {
  font-size: 12px;
  font-weight: 600;
  color: var(--text-muted);
  user-select: none;
}

/* Animations */
@keyframes correctFlash {
  0% { background: rgba(22, 163, 74, 0.3); }
  100% { background: rgba(22, 163, 74, 0.1); }
}

@keyframes incorrectFlash {
  0% { background: rgba(220, 38, 38, 0.3); }
  50% { background: rgba(220, 38, 38, 0.2); }
  100% { background: rgba(220, 38, 38, 0.05); }
}

/* ── Study Tooltip ── */

.study-tooltip {
  position: fixed;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  padding: 10px 14px;
  box-shadow: var(--popup-shadow);
  z-index: 200;
  max-width: 280px;
  font-size: 13px;
}

.study-tooltip-header {
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 2px;
}

.study-tooltip-section {
  color: var(--text-muted);
  font-size: 12px;
  margin-bottom: 6px;
}

.study-tooltip-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
}

.tag {
  font-size: 11px;
  padding: 2px 8px;
  background: var(--accent-light);
  border-radius: 10px;
  color: var(--accent);
  font-weight: 500;
}

/* ── Reveal Popup ── */

.reveal-popup {
  position: fixed;
  z-index: 300;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 14px;
  box-shadow: var(--popup-shadow);
  width: 340px;
  max-width: 90vw;
  overflow: hidden;
}

.reveal-popup-content {
  padding: 0;
}

.reveal-popup-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 16px;
  border-bottom: 1px solid var(--border-color);
  background: var(--bg-secondary);
}

.reveal-popup-section {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-primary);
}

.reveal-popup-close {
  background: none;
  border: none;
  font-size: 20px;
  cursor: pointer;
  color: var(--text-muted);
  line-height: 1;
  padding: 0 4px;
}

.reveal-popup-close:hover {
  color: var(--text-primary);
}

.reveal-popup-body {
  padding: 16px;
}

.reveal-think {
  text-align: center;
  margin-bottom: 12px;
}

.reveal-think p {
  color: var(--text-secondary);
  font-size: 14px;
  margin-bottom: 8px;
}

.hint-btn {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  padding: 4px 12px;
  border-radius: 4px;
  font-size: 12px;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
}

.hint-btn:hover {
  background: var(--bg-secondary);
  color: var(--text-primary);
}

.hint-text {
  margin-top: 8px;
  padding: 8px 12px;
  background: linear-gradient(135deg, #fef3c7, #fde68a);
  border-radius: 8px;
  font-size: 13px;
  color: #92400e;
  border: 1px solid #fcd34d;
}

body.dark-mode .hint-text {
  background: linear-gradient(135deg, #451a03, #78350f);
  color: #fbbf24;
  border-color: #b45309;
}

.reveal-actions-pre {
  text-align: center;
}

.btn-reveal {
  padding: 8px 28px;
  background: var(--gradient-accent);
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  box-shadow: 0 2px 8px var(--accent-glow);
}

.btn-reveal:hover {
  filter: brightness(1.1);
  box-shadow: 0 4px 14px var(--accent-glow);
  transform: translateY(-1px);
}

.reveal-formula {
  text-align: center;
  padding: 16px 8px;
  margin-bottom: 12px;
  background: var(--bg-secondary);
  border-radius: 8px;
  overflow-x: auto;
}

.reveal-actions {
  display: flex;
  gap: 8px;
}

.btn-grade {
  flex: 1;
  padding: 10px 16px;
  border: none;
  border-radius: 6px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  transition: all var(--transition);
}

.btn-got-it {
  background: linear-gradient(135deg, #d1fae5, #a7f3d0);
  color: #065f46;
  border: 1px solid #6ee7b7;
}

.btn-got-it:hover {
  background: linear-gradient(135deg, #a7f3d0, #6ee7b7);
  transform: translateY(-1px);
  box-shadow: 0 2px 8px rgba(5, 150, 105, 0.2);
}

body.dark-mode .btn-got-it {
  background: linear-gradient(135deg, #064e3b, #065f46);
  color: #6ee7b7;
  border-color: #059669;
}

.btn-missed-it {
  background: linear-gradient(135deg, #fee2e2, #fecaca);
  color: #991b1b;
  border: 1px solid #fca5a5;
}

.btn-missed-it:hover {
  background: linear-gradient(135deg, #fecaca, #fca5a5);
  transform: translateY(-1px);
  box-shadow: 0 2px 8px rgba(220, 38, 38, 0.2);
}

body.dark-mode .btn-missed-it {
  background: linear-gradient(135deg, #450a0a, #7f1d1d);
  color: #fca5a5;
  border-color: #dc2626;
}

.grade-icon {
  font-size: 16px;
}

/* ── Session Summary Modal ── */

.session-summary-modal {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0,0,0,0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 500;
}

.session-summary {
  background: var(--bg-primary);
  border-radius: 18px;
  padding: 32px;
  max-width: 420px;
  width: 90%;
  box-shadow: var(--popup-shadow);
  text-align: center;
  border: 1px solid var(--border-color);
}

.session-summary h2 {
  margin-bottom: 20px;
  font-size: 22px;
  color: var(--accent);
}

.summary-score {
  margin-bottom: 20px;
}

.score-circle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 100px;
  height: 100px;
  border-radius: 50%;
  border: 4px solid;
}

.score-circle.score-great {
  border-color: var(--correct-color);
  background: var(--correct-bg);
}

.score-circle.score-good {
  border-color: var(--reviewing-color);
  background: rgba(245, 158, 11, 0.1);
}

.score-circle.score-needs-work {
  border-color: var(--incorrect-color);
  background: var(--incorrect-bg);
}

.score-number {
  font-size: 28px;
  font-weight: 700;
}

.summary-details {
  display: flex;
  justify-content: center;
  gap: 24px;
  margin-bottom: 20px;
}

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

.summary-label {
  display: block;
  font-size: 12px;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.summary-value {
  font-size: 24px;
  font-weight: 600;
}

.summary-value.correct {
  color: var(--correct-color);
}

.summary-value.incorrect {
  color: var(--incorrect-color);
}

.summary-missed {
  text-align: left;
  margin-bottom: 20px;
  max-height: 150px;
  overflow-y: auto;
}

.summary-missed h3 {
  font-size: 14px;
  color: var(--text-secondary);
  margin-bottom: 8px;
}

.summary-missed ul {
  list-style: none;
  padding: 0;
}

.summary-missed li {
  padding: 4px 0;
  font-size: 13px;
  border-bottom: 1px solid var(--border-color);
}

.summary-perfect {
  color: var(--correct-color);
  font-weight: 500;
  margin-bottom: 20px;
}

.summary-actions {
  display: flex;
  gap: 8px;
  justify-content: center;
}

/* ── Buttons ── */

.btn-primary {
  padding: 8px 20px;
  background: var(--gradient-accent);
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  box-shadow: 0 2px 8px var(--accent-glow);
}

.btn-primary:hover {
  filter: brightness(1.1);
  box-shadow: 0 4px 14px var(--accent-glow);
  transform: translateY(-1px);
}

.btn-primary.btn-small {
  padding: 4px 12px;
  font-size: 13px;
}

body.dark-mode .btn-primary {
  background: linear-gradient(135deg, #B1CDE5, #8ab0d0);
  color: #0b1929;
}

body.dark-mode .btn-reveal {
  background: linear-gradient(135deg, #B1CDE5, #8ab0d0);
  color: #0b1929;
}

.btn-secondary {
  padding: 8px 20px;
  background: var(--bg-primary);
  color: var(--accent);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
}

.btn-secondary:hover {
  background: var(--accent-light);
  border-color: var(--accent);
}

.btn-danger {
  padding: 8px 20px;
  background: #fef2f2;
  color: #991b1b;
  border: 1px solid #fecaca;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
}

.btn-danger:hover {
  background: #fee2e2;
  transform: translateY(-1px);
}

body.dark-mode .btn-danger {
  background: #450a0a;
  color: #fca5a5;
  border-color: #7f1d1d;
}

/* ── Side Panels (Settings & Stats) ── */

.side-panel {
  position: fixed;
  top: 0;
  right: -420px;
  width: 400px;
  max-width: 90vw;
  height: 100vh;
  background: var(--bg-primary);
  box-shadow: var(--panel-shadow);
  z-index: 400;
  overflow-y: auto;
  transition: right 0.3s ease;
  border-left: 1px solid var(--border-color);
}

.side-panel.visible {
  right: 0;
}

.settings-content, .stats-content {
  padding: 20px;
}

.settings-header, .stats-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

.settings-header h2, .stats-header h2 {
  font-size: 18px;
}

.settings-close, .stats-close {
  background: none;
  border: none;
  font-size: 24px;
  cursor: pointer;
  color: var(--text-muted);
}

.settings-close:hover, .stats-close:hover {
  color: var(--text-primary);
}

.settings-group {
  margin-bottom: 24px;
}

.settings-group h3 {
  font-size: 12px;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 12px;
  font-weight: 700;
}

.setting-item {
  margin-bottom: 16px;
}

.setting-item > label {
  display: block;
  font-size: 14px;
  font-weight: 500;
  margin-bottom: 6px;
  color: var(--text-primary);
}

.checkbox-label {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 14px;
  cursor: pointer;
  color: var(--text-primary);
}

.checkbox-label input[type="checkbox"] {
  width: 16px;
  height: 16px;
  accent-color: var(--accent);
}

.level-selector {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.level-selector input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}

.level-display {
  font-size: 13px;
  color: var(--text-secondary);
}

.blanking-override {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.setting-actions {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

/* ── Stats Panel ── */

.stats-overview {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-bottom: 20px;
}

.stat-card {
  padding: 14px;
  background: var(--bg-secondary);
  border-radius: 10px;
  text-align: center;
  border: 1px solid var(--border-color);
  transition: all var(--transition);
}

.stat-card:hover {
  box-shadow: 0 2px 12px var(--accent-glow);
  border-color: var(--accent);
}

.stat-number {
  font-size: 28px;
  font-weight: 700;
  color: var(--accent);
}

.stat-label {
  font-size: 12px;
  color: var(--text-muted);
  margin-bottom: 6px;
}

.stat-bar {
  height: 4px;
  background: var(--bg-tertiary);
  border-radius: 2px;
  overflow: hidden;
}

.stat-bar-fill {
  height: 100%;
  border-radius: 2px;
  transition: width 0.3s ease;
}

.stat-bar-fill.mastered { background: var(--mastered-color); }
.stat-bar-fill.reviewing { background: var(--reviewing-color); }
.stat-bar-fill.learning { background: var(--learning-color); }
.stat-bar-fill.not-started { background: var(--not-started-color); }

.stats-streak {
  text-align: center;
  padding: 14px;
  background: linear-gradient(135deg, var(--bg-secondary), var(--bg-tertiary));
  border-radius: 10px;
  margin-bottom: 16px;
  font-size: 16px;
  border: 1px solid var(--border-color);
}

.streak-flame {
  font-size: 20px;
  margin-right: 6px;
}

.streak-count {
  font-weight: 600;
}

.stats-level {
  display: flex;
  justify-content: space-between;
  padding: 12px 16px;
  background: var(--bg-secondary);
  border-radius: 10px;
  margin-bottom: 20px;
  font-size: 14px;
  border: 1px solid var(--border-color);
}

.stats-sections {
  margin-bottom: 20px;
}

.stats-sections h3, .stats-heatmap h3, .stats-history h3, .stats-due h3 {
  font-size: 12px;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 10px;
  font-weight: 700;
}

.section-breakdown {
  margin-bottom: 8px;
}

.section-name {
  font-size: 13px;
  font-weight: 500;
  margin-bottom: 4px;
}

.section-bar-container {
  display: flex;
  align-items: center;
  gap: 8px;
}

.section-bar {
  flex: 1;
  height: 6px;
  background: var(--bg-tertiary);
  border-radius: 3px;
  overflow: hidden;
  display: flex;
}

.section-bar-mastered { background: var(--mastered-color); }
.section-bar-reviewing { background: var(--reviewing-color); }
.section-bar-learning { background: var(--learning-color); }

.section-count {
  font-size: 12px;
  color: var(--text-muted);
  white-space: nowrap;
}

/* ── Heatmap ── */

.heatmap-pages {
  display: flex;
  gap: 12px;
}

.heatmap-page {
  flex: 1;
}

.heatmap-label {
  font-size: 12px;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.heatmap-grid {
  position: relative;
  height: 120px;
  background: var(--bg-secondary);
  border-radius: 8px;
  border: 1px solid var(--border-color);
}

.heatmap-dot {
  position: absolute;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  transform: translate(-50%, -50%);
}

.heatmap-dot.mastered { background: var(--mastered-color); }
.heatmap-dot.reviewing { background: var(--reviewing-color); }
.heatmap-dot.learning { background: var(--learning-color); }
.heatmap-dot.not-started { background: var(--not-started-color); }

/* ── Session History ── */

.session-list {
  max-height: 200px;
  overflow-y: auto;
}

.session-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 6px 0;
  border-bottom: 1px solid var(--border-color);
  font-size: 13px;
}

.session-date {
  color: var(--text-muted);
  white-space: nowrap;
}

.session-mode {
  background: var(--accent-light);
  color: var(--accent);
  padding: 2px 8px;
  border-radius: 10px;
  font-size: 11px;
  text-transform: capitalize;
  font-weight: 500;
}

.session-score {
  font-weight: 600;
  margin-left: auto;
}

.session-score.score-great { color: var(--correct-color); }
.session-score.score-good { color: var(--reviewing-color); }
.session-score.score-needs-work { color: var(--incorrect-color); }

.session-detail {
  color: var(--text-muted);
  font-size: 12px;
}

.no-sessions {
  color: var(--text-muted);
  font-size: 13px;
  font-style: italic;
}

.stats-due {
  margin-bottom: 20px;
}

.stats-due p {
  font-size: 14px;
  color: var(--text-secondary);
}

/* ── Welcome Overlay ── */

.welcome-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0,0,0,0.6);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 600;
  animation: fadeIn 0.3s ease;
}

.welcome-overlay.fading-out {
  animation: fadeOut 0.3s ease;
  opacity: 0;
}

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

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

.welcome-content {
  background: var(--bg-primary);
  border-radius: 18px;
  padding: 40px;
  max-width: 600px;
  width: 90%;
  box-shadow: var(--popup-shadow);
  border: 1px solid var(--border-color);
}

.welcome-content h1 {
  font-size: 26px;
  margin-bottom: 8px;
  background: var(--gradient-accent);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.welcome-content > p {
  color: var(--text-secondary);
  font-size: 15px;
  margin-bottom: 24px;
}

.welcome-modes {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 24px;
}

.welcome-mode {
  padding: 14px 18px;
  background: var(--bg-secondary);
  border-radius: 10px;
  border: 1px solid var(--border-color);
  transition: all var(--transition);
}

.welcome-mode:hover {
  border-color: var(--accent);
  box-shadow: 0 2px 12px var(--accent-glow);
}

.welcome-mode h3 {
  font-size: 15px;
  margin-bottom: 4px;
  color: var(--accent);
  font-weight: 600;
}

.welcome-mode p {
  font-size: 13px;
  color: var(--text-secondary);
}

.welcome-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* ── PDF Error ── */

.pdf-error {
  text-align: center;
  padding: 60px 40px;
  max-width: 500px;
}

.pdf-error h2 {
  color: var(--incorrect-color);
  margin-bottom: 12px;
}

.pdf-error p {
  color: var(--text-secondary);
  margin-bottom: 16px;
}

.pdf-error ul {
  text-align: left;
  color: var(--text-secondary);
  font-size: 14px;
}

.pdf-error code {
  background: var(--bg-tertiary);
  padding: 2px 6px;
  border-radius: 3px;
  font-family: var(--font-mono);
  font-size: 13px;
}

/* ── Responsive ── */

@media (max-width: 1200px) {
  .app-title {
    display: none;
  }
}

@media (max-width: 900px) {
  .top-bar {
    flex-wrap: wrap;
    height: auto;
    gap: 8px;
    padding: 8px 12px;
  }

  .mode-btn {
    padding: 4px 10px;
    font-size: 12px;
  }

  #sheet-container {
    padding: 10px;
  }
}