/* ══════════════════════════════════════════
   STAR TREK THEME — SHARED CSS
   Holland Academy · AP Physics Platform
   ══════════════════════════════════════════ */

/* ── Page Load Fade ── */
body { opacity: 0; transition: opacity 0.3s ease; }
body.loaded { opacity: 1; }

:root {
  --trek-gold: #f0a500;
  --trek-gold-dim: #c28700;
  --trek-blue: #4fc3f7;
  --trek-blue-dark: #0288d1;
  --trek-blue-glow: rgba(79,195,247,0.3);
  --trek-red: #ff5252;
  --trek-red-glow: rgba(255,82,82,0.3);
  --trek-green: #69f0ae;
  --trek-green-glow: rgba(105,240,174,0.3);
  --trek-purple: #b388ff;
  --trek-orange: #ffab40;
  --bg-deep: #0a0e1a;
  --bg-panel: #101728;
  --bg-card: #151d30;
  --bg-card-hover: #1a2440;
  --border-subtle: rgba(79,195,247,0.15);
  --border-glow: rgba(79,195,247,0.4);
  --text-primary: #e8eaf6;
  --text-secondary: #90a4ae;
  --text-dim: #78909c;
  --font-display: 'Orbitron', sans-serif;
  --font-body: 'Rajdhani', sans-serif;
  --font-mono: 'Share Tech Mono', monospace;
  --radius: 8px;
  --radius-lg: 16px;
}

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

html, body {
  height: 100%;
  overflow: hidden;
}

body {
  font-family: var(--font-body);
  background: var(--bg-deep);
  color: var(--text-primary);
  line-height: 1.6;
}

/* ── Accessibility ── */
:focus-visible {
  outline: 2px solid var(--trek-blue);
  outline-offset: 2px;
  box-shadow: 0 0 8px var(--trek-blue-glow);
}

.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

#a11y-feedback {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* ── Starfield Background ── */
.starfield {
  position: fixed;
  inset: 0;
  z-index: 0;
  overflow: hidden;
  pointer-events: none;
}

.star {
  position: absolute;
  width: 2px;
  height: 2px;
  background: white;
  border-radius: 50%;
  animation: twinkle var(--dur) ease-in-out infinite alternate;
}

@keyframes twinkle {
  0% { opacity: 0.2; transform: scale(0.8); }
  100% { opacity: 1; transform: scale(1.2); }
}

/* ── LCARS-style Header ── */
.lcars-header {
  position: relative;
  z-index: 10;
  display: flex;
  align-items: stretch;
  height: 64px;
  background: var(--bg-panel);
  border-bottom: 2px solid var(--border-subtle);
}

.lcars-elbow {
  width: 80px;
  background: var(--trek-gold);
  border-radius: 0 0 32px 0;
  position: relative;
}

.lcars-elbow::after {
  content: '';
  position: absolute;
  right: -1px;
  bottom: 0;
  width: 32px;
  height: 100%;
  background: var(--bg-panel);
  border-radius: 0 0 0 32px;
}

.lcars-bar {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px 0 40px;
  gap: 16px;
}

.lcars-title {
  display: flex;
  align-items: center;
  gap: 16px;
}

.lcars-title h1 {
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--trek-gold);
}

.lcars-title .divider {
  width: 1px;
  height: 24px;
  background: var(--border-subtle);
}

.lcars-title .subtitle {
  font-family: var(--font-body);
  font-size: 15px;
  color: var(--text-secondary);
  font-weight: 500;
}

.lcars-status {
  display: flex;
  align-items: center;
  gap: 20px;
}

.lcars-indicator {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 13px;
}

.lcars-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  animation: pulse 2s ease-in-out infinite;
}

.lcars-dot.green { background: var(--trek-green); box-shadow: 0 0 8px var(--trek-green-glow); }
.lcars-dot.blue { background: var(--trek-blue); box-shadow: 0 0 8px var(--trek-blue-glow); }

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.4; }
}

/* ── Mobile Nav (hidden by default) ── */
.mobile-nav {
  display: none;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--trek-green);
}

.mobile-nav a {
  color: var(--trek-gold);
  text-decoration: none;
  font-size: 16px;
}

/* ── Home Button (injected by app.js on every lesson/homework page) ── */
.btn-home {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin-left: 16px;
  padding: 6px 14px;
  background: rgba(79, 195, 247, 0.12);
  color: var(--trek-gold);
  border: 1px solid rgba(240, 165, 0, 0.55);
  border-radius: 6px;
  font-family: var(--font-display);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  cursor: pointer;
  transition: background 0.2s ease, border-color 0.2s ease, color 0.2s ease;
  flex-shrink: 0;
  align-self: center;
}

.btn-home:hover,
.btn-home:focus-visible {
  background: rgba(240, 165, 0, 0.18);
  border-color: var(--trek-gold);
  color: #fff;
  outline: none;
}

.btn-home-icon { font-size: 16px; line-height: 1; }

/* When injected into the mobile-nav host (narrow screens), it sits inline with the counter. */
.mobile-nav .btn-home { margin-left: 4px; }

/* ── Progress Bar ── */
.progress-container {
  display: flex;
  align-items: center;
  gap: 12px;
}

.progress-label {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--trek-blue);
  white-space: nowrap;
}

.progress-track {
  width: 140px;
  height: 4px;
  background: rgba(79,195,247,0.15);
  border-radius: 2px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--trek-blue), var(--trek-green));
  border-radius: 2px;
  transition: width 0.3s ease;
}

/* ── Main Container ── */
.main-wrapper {
  position: relative;
  z-index: 1;
  display: flex;
  flex-direction: column;
  height: 100%;
}

/* ── Slide Viewport ── */
/* Homework style: scrollable flex container */
.slide-viewport {
  flex: 1;
  overflow-y: auto;
  overflow-x: hidden;
  padding: 24px;
  display: flex;
  align-items: stretch;
  justify-content: center;
}

.slide-viewport::-webkit-scrollbar {
  width: 8px;
}

.slide-viewport::-webkit-scrollbar-track {
  background: rgba(79,195,247,0.1);
}

.slide-viewport::-webkit-scrollbar-thumb {
  background: rgba(79,195,247,0.3);
  border-radius: 4px;
}

.slide-viewport::-webkit-scrollbar-thumb:hover {
  background: rgba(79,195,247,0.5);
}

/* ── Slide Container (homework) ── */
.slide-container {
  width: 100%;
  max-width: 900px;
  background: rgba(16, 23, 40, 0.85);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 40px;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(8px);
  transition: opacity 0.2s ease;
}

.slide-container.fading { opacity: 0; }

/* ── Slide (lesson) ── */
.slide {
  display: none;
  width: 100%;
  max-width: 900px;
  animation: slideIn 0.5s ease;
}

.slide.active { display: block; }

@keyframes slideIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ── Slide Card (lesson) ── */
.slide-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 40px;
  position: relative;
  overflow: hidden;
  max-height: calc(100vh - 140px);
  overflow-y: auto;
}

.slide-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--trek-gold), var(--trek-blue), var(--trek-purple));
}

.slide-card::-webkit-scrollbar { width: 6px; }
.slide-card::-webkit-scrollbar-track { background: transparent; }
.slide-card::-webkit-scrollbar-thumb { background: var(--border-subtle); border-radius: 3px; }

/* ── Slide Badge (lesson) ── */
.slide-badge {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--trek-gold);
  text-transform: uppercase;
  letter-spacing: 2px;
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.slide-badge .badge-icon {
  width: 18px;
  height: 18px;
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 10px;
}

.badge-lesson .badge-icon { background: var(--trek-blue); color: var(--bg-deep); }
.badge-question .badge-icon { background: var(--trek-gold); color: var(--bg-deep); }
.badge-interactive .badge-icon { background: var(--trek-purple); color: var(--bg-deep); }
.badge-challenge .badge-icon { background: var(--trek-red); color: var(--bg-deep); }

/* ── Badge System (homework) ── */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  padding: 4px 10px;
  border-radius: 4px;
  margin-bottom: 12px;
}

.badge-homework {
  background: rgba(255, 171, 64, 0.15);
  color: var(--trek-orange);
  border: 1px solid rgba(255, 171, 64, 0.25);
}

.badge-difficulty {
  background: rgba(180, 136, 255, 0.15);
  color: var(--trek-purple);
  border: 1px solid rgba(180, 136, 255, 0.25);
  margin-left: 8px;
}

/* ── Title & Content ── */
.slide-title {
  font-family: var(--font-display);
  font-size: 28px;
  font-weight: 700;
  letter-spacing: 1px;
  margin-bottom: 20px;
  color: var(--trek-gold);
}

.slide-body {
  font-size: 15px;
  line-height: 1.8;
  color: var(--text-secondary);
  margin-bottom: 20px;
}

.slide-body p {
  margin-bottom: 14px;
}

.slide-body ul {
  margin: 14px 0 14px 24px;
  list-style: none;
}

.slide-body ul li {
  position: relative;
  padding-left: 20px;
  margin-bottom: 10px;
}

.slide-body ul li::before {
  content: '⬢';
  position: absolute;
  left: 0;
  color: var(--trek-blue);
  font-size: 10px;
}

.slide-body strong { color: var(--trek-blue); font-weight: 700; }
.slide-body em { color: var(--trek-gold); font-style: normal; font-weight: 600; }

/* ── Equation Display ── */
.equation-display {
  background: rgba(79,195,247,0.06);
  border: 1px solid var(--border-subtle);
  border-left: 3px solid var(--trek-blue);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 20px 24px;
  margin: 20px 0;
  text-align: center;
}

.equation-display .eq-label {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--trek-blue);
  text-transform: uppercase;
  letter-spacing: 1.5px;
  margin-bottom: 10px;
  display: block;
}

.equation-display .katex { font-size: 1.4em !important; color: var(--text-primary); }

.equation-display.highlight {
  border-left-color: var(--trek-gold);
  background: rgba(240,165,0,0.06);
}

.equation-display.highlight .eq-label { color: var(--trek-gold); }

/* ── Info Boxes ── */
.info-box {
  background: rgba(79, 195, 247, 0.06);
  border-left: 3px solid var(--trek-blue);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 14px 18px;
  margin: 16px 0;
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.7;
}

.info-box.tip {
  background: rgba(105,240,174,0.08);
  border: 1px solid rgba(105,240,174,0.25);
  color: var(--trek-green);
}

.info-box.warning {
  background: rgba(255,82,82,0.08);
  border: 1px solid rgba(255,82,82,0.25);
  color: var(--trek-red);
}

.info-box.note {
  background: rgba(179,136,255,0.08);
  border: 1px solid rgba(179,136,255,0.25);
  color: var(--trek-purple);
}

.info-box .box-title {
  font-weight: 700;
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 6px;
  color: var(--text-primary);
}

/* ── Bullet Points ── */
.trek-list {
  list-style: none;
  margin: 16px 0;
}

.trek-list li {
  padding: 8px 0 8px 24px;
  position: relative;
  color: var(--text-secondary);
  font-size: 15px;
}

.trek-list li::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--trek-blue);
  font-weight: 700;
}

/* ── Scenario Box ── */
.scenario {
  background: rgba(79,195,247,0.05);
  border-left: 3px solid var(--trek-blue);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 16px 20px;
  margin: 16px 0;
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.8;
}

/* ── Diagram Container ── */
.diagram-container {
  background: rgba(79, 195, 247, 0.03);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  padding: 20px;
  margin: 16px 0;
  text-align: center;
}

.diagram-container svg {
  max-width: 100%;
  height: auto;
}

.diagram-caption {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--text-dim);
  margin-top: 10px;
}

/* ── Slider Control ── */
.slider-group {
  display: flex;
  align-items: center;
  gap: 16px;
  justify-content: center;
  margin-top: 14px;
  flex-wrap: wrap;
}

.slider-group label {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--text-secondary);
}

input[type="range"] {
  -webkit-appearance: none;
  width: 200px;
  height: 4px;
  background: var(--border-subtle);
  border-radius: 2px;
  outline: none;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--trek-blue);
  cursor: pointer;
  box-shadow: 0 0 8px var(--trek-blue-glow);
}

input[type="range"]::-moz-range-thumb {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--trek-blue);
  cursor: pointer;
  box-shadow: 0 0 8px var(--trek-blue-glow);
  border: none;
}

.slider-value {
  font-family: var(--font-mono);
  font-size: 15px;
  font-weight: 700;
  color: var(--trek-gold);
  min-width: 60px;
}

.density-output {
  margin-top: 12px;
  font-family: var(--font-mono);
  font-size: 15px;
  color: var(--text-primary);
  text-align: center;
}

.density-status {
  margin-top: 8px;
  font-size: 14px;
  font-family: var(--font-body);
  font-weight: 600;
}

.density-status.denser { color: var(--trek-red); }
.density-status.less-dense { color: var(--trek-blue); }
.density-status.same { color: var(--trek-green); }

/* ── Question Styles ── */
.q-options {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin: 20px 0;
}

.q-option {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 14px 18px;
  background: rgba(255,255,255,0.03);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  cursor: pointer;
  transition: all 0.25s ease;
  font-size: 15px;
  color: var(--text-secondary);
  font-family: var(--font-body);
  font-weight: 500;
  text-align: left;
  width: 100%;
}

.q-option:hover:not(:disabled):not(.locked) {
  border-color: var(--trek-blue);
  background: rgba(79,195,247,0.06);
  color: var(--text-primary);
}

.q-option .letter {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: 2px solid var(--border-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-display);
  font-size: 12px;
  font-weight: 700;
  flex-shrink: 0;
  transition: all 0.25s;
}

.q-option:hover:not(:disabled):not(.locked) .letter {
  border-color: var(--trek-blue);
  color: var(--trek-blue);
}

.q-option.selected {
  border-color: var(--trek-blue);
  background: rgba(79,195,247,0.1);
}

.q-option.selected .letter {
  background: var(--trek-blue);
  border-color: var(--trek-blue);
  color: var(--bg-deep);
}

.q-option.correct-reveal {
  border-color: var(--trek-green);
  background: rgba(105,240,174,0.1);
}

.q-option.correct-reveal .letter {
  background: var(--trek-green);
  border-color: var(--trek-green);
  color: var(--bg-deep);
}

.q-option.wrong-reveal {
  border-color: var(--trek-red);
  background: rgba(255,82,82,0.08);
}

.q-option.wrong-reveal .letter {
  background: var(--trek-red);
  border-color: var(--trek-red);
  color: var(--bg-deep);
}

.q-option.locked { cursor: default; }

.q-option.eliminated {
  opacity: 0.4;
  cursor: default;
  pointer-events: none;
}

/* ── Calc Input ── */
.calc-group {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 20px 0;
  flex-wrap: wrap;
}

.calc-input {
  flex: 1;
  min-width: 140px;
  padding: 12px 16px;
  background: rgba(255,255,255,0.05);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 16px;
  transition: border-color 0.2s;
}

.calc-input:focus {
  outline: none;
  border-color: var(--trek-blue);
  box-shadow: 0 0 0 3px var(--trek-blue-glow);
}

.calc-input.correct { border-color: var(--trek-green); }
.calc-input.incorrect { border-color: var(--trek-red); }
.calc-input:disabled { opacity: 0.6; cursor: default; }

.calc-unit {
  font-family: var(--font-mono);
  color: var(--text-dim);
  font-size: 14px;
}

/* ── True/False Buttons ── */
.tf-group {
  display: flex;
  gap: 16px;
  margin: 20px 0;
}

.tf-btn {
  flex: 1;
  padding: 18px;
  background: rgba(255,255,255,0.03);
  border: 2px solid var(--border-subtle);
  border-radius: var(--radius);
  color: var(--text-secondary);
  font-family: var(--font-display);
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.25s;
  letter-spacing: 1px;
}

.tf-btn:hover:not(:disabled) {
  border-color: var(--trek-blue);
  background: rgba(79,195,247,0.06);
  color: var(--text-primary);
}

.tf-btn.selected { border-color: var(--trek-blue); background: rgba(79,195,247,0.1); color: var(--trek-blue); }
.tf-btn.correct-reveal { border-color: var(--trek-green); background: rgba(105,240,174,0.1); color: var(--trek-green); }
.tf-btn.wrong-reveal { border-color: var(--trek-red); background: rgba(255,82,82,0.08); color: var(--trek-red); }
.tf-btn:disabled { cursor: default; }

/* ── Action Buttons ── */
.btn-row {
  display: flex;
  gap: 12px;
  margin-top: 20px;
  flex-wrap: wrap;
}

.btn {
  padding: 10px 24px;
  border-radius: var(--radius);
  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.25s;
  border: none;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  letter-spacing: 0.5px;
}

.btn-primary {
  background: linear-gradient(135deg, var(--trek-blue-dark), var(--trek-blue));
  color: white;
  box-shadow: 0 0 12px var(--trek-blue-glow);
}

.btn-primary:hover { box-shadow: 0 0 20px var(--trek-blue-glow); transform: translateY(-1px); }

.btn-submit {
  background: linear-gradient(135deg, var(--trek-gold-dim), var(--trek-gold));
  color: var(--bg-deep);
  font-weight: 800;
}

.btn-submit:hover:not(:disabled) { box-shadow: 0 0 16px rgba(240,165,0,0.4); transform: translateY(-1px); }
.btn-submit:disabled { opacity: 0.4; cursor: default; transform: none; box-shadow: none; }

.btn-hint {
  background: rgba(240,165,0,0.15);
  border: 1px solid rgba(240,165,0,0.3);
  color: var(--trek-gold);
}

.btn-hint:hover { background: rgba(240,165,0,0.25); }

/* ── Navigation ── */
.slide-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 24px;
  padding-top: 20px;
  border-top: 1px solid var(--border-subtle);
}

.nav-btn {
  padding: 10px 28px;
  border-radius: var(--radius);
  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.25s;
  border: 1px solid var(--border-subtle);
  background: transparent;
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-btn:hover:not(:disabled) {
  border-color: var(--trek-blue);
  color: var(--trek-blue);
  background: rgba(79,195,247,0.06);
}

.nav-btn:disabled { opacity: 0.3; cursor: default; }

.nav-btn.next {
  background: linear-gradient(135deg, var(--trek-blue-dark), var(--trek-blue));
  color: white;
  border: none;
  box-shadow: 0 0 12px var(--trek-blue-glow);
}

.nav-btn.next:hover:not(:disabled) { box-shadow: 0 0 20px var(--trek-blue-glow); transform: translateY(-1px); }
.nav-btn.next:disabled { opacity: 0.3; box-shadow: none; transform: none; }

.slide-counter {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--text-dim);
}

/* ── Feedback ── */
.feedback {
  padding: 16px 20px;
  border-radius: var(--radius);
  margin-top: 16px;
  font-size: 14px;
  line-height: 1.7;
  animation: feedbackIn 0.4s ease;
}

@keyframes feedbackIn {
  from { opacity: 0; transform: translateY(-10px); }
  to { opacity: 1; transform: translateY(0); }
}

.feedback.correct {
  background: rgba(105,240,174,0.1);
  border: 1px solid rgba(105,240,174,0.3);
  color: var(--trek-green);
}

.feedback.incorrect {
  background: rgba(255,82,82,0.1);
  border: 1px solid rgba(255,82,82,0.3);
  color: var(--trek-red);
}

.feedback .fb-title {
  font-weight: 700;
  font-size: 15px;
  margin-bottom: 6px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.feedback .fb-explain {
  color: var(--text-secondary);
  font-size: 14px;
  margin-top: 8px;
  padding-top: 8px;
  border-top: 1px solid rgba(255,255,255,0.06);
}

/* ── Hint ── */
.hint-box {
  background: rgba(240,165,0,0.08);
  border: 1px solid rgba(240,165,0,0.25);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin-top: 12px;
  color: var(--trek-gold);
  font-size: 14px;
  animation: feedbackIn 0.3s ease;
}

.hint-box .hint-label {
  font-weight: 700;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 4px;
}

/* ── Score Screen ── */
.score-screen {
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 20px;
  min-height: 400px;
  padding: 20px 0;
}

.score-ring {
  position: relative;
  width: 200px;
  height: 200px;
  border-radius: 50%;
  background: conic-gradient(var(--trek-green) 0deg, var(--trek-green) var(--score-angle, 0deg), rgba(79,195,247,0.1) var(--score-angle, 0deg), rgba(79,195,247,0.1) 360deg);
  border: 3px solid var(--trek-blue);
  box-shadow: 0 0 24px var(--trek-blue-glow);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  animation: scoreReveal 0.8s ease-out forwards;
}

.score-ring::before {
  content: '';
  position: absolute;
  inset: -4px;
  border-radius: 50%;
  border: 4px solid transparent;
  border-top-color: var(--trek-gold);
  border-right-color: var(--trek-blue);
  animation: spin 3s linear infinite;
}

@keyframes spin { to { transform: rotate(360deg); } }

@keyframes scoreReveal { from { --score-angle: 0deg; } }

.score-num {
  font-family: var(--font-display);
  font-size: 48px;
  font-weight: 900;
  color: var(--trek-green);
  text-shadow: 0 0 16px var(--trek-green-glow);
}

.score-of {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--text-secondary);
}

.score-screen h3 {
  font-family: var(--font-display);
  font-size: 24px;
  color: var(--trek-gold);
  letter-spacing: 1px;
}

.score-screen p {
  font-size: 15px;
  color: var(--text-secondary);
  max-width: 500px;
  line-height: 1.8;
  margin: 0 auto 24px;
}

.score-screen .rank {
  font-family: var(--font-display);
  font-size: 20px;
  color: var(--trek-orange);
  letter-spacing: 2px;
  margin-bottom: 10px;
}

.btn-home {
  background: linear-gradient(135deg, var(--trek-blue-dark), var(--trek-blue));
  color: white;
  border: none;
  box-shadow: 0 0 12px var(--trek-blue-glow);
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin-top: 8px;
}

.btn-home:hover {
  box-shadow: 0 0 20px var(--trek-blue-glow);
  transform: translateY(-1px);
}

/* ── KaTeX Dark Theme ── */
.katex { color: var(--text-primary) !important; }
.katex .mord, .katex .mbin, .katex .mrel, .katex .mop { color: var(--text-primary) !important; }

/* ── Responsive Breakpoint ── */
@media (max-width: 768px) {
  .lcars-elbow { display: none; }
  .lcars-header { height: 40px; }
  .lcars-bar { padding: 0 12px; }
  .lcars-title h1,
  .lcars-title .divider { display: none; }
  .lcars-title .subtitle { font-size: 13px; }
  .lcars-status .progress-container { display: none; }
  .lcars-status .lcars-indicator { display: none; }
  .mobile-nav { display: flex; }

  .btn-home {
    margin-left: 8px;
    padding: 6px 10px;
    font-size: 10px;
    letter-spacing: 1px;
  }
  .btn-home-label { display: none; }
  .btn-home-icon { font-size: 18px; }

  .slide-viewport { height: calc(100vh - 40px); padding: 12px; }
  .slide-container { padding: 16px; }
  .slide-card { padding: 16px; }
  .slide-title { font-size: 20px; }

  .q-option { padding: 14px 16px; min-height: 44px; }
  .btn, .nav-btn { min-height: 44px; }
  .calc-input { min-height: 44px; }

  .score-ring { width: 140px; height: 140px; }
  .score-num { font-size: 36px; }
}

/* ══════════════════════════════════════════
   SHOW ANSWER + "Answer Revealed" feedback
   ══════════════════════════════════════════ */

.btn-show-answer {
  background: rgba(255,171,64,0.14);
  border: 1px solid rgba(255,171,64,0.35);
  color: var(--trek-orange);
}

.btn-show-answer:hover {
  background: rgba(255,171,64,0.22);
  box-shadow: 0 0 12px rgba(255,171,64,0.3);
}

.feedback.shown {
  background: rgba(255,171,64,0.08);
  border: 1px solid rgba(255,171,64,0.28);
  color: var(--trek-orange);
}

.calc-input.shown {
  border-color: var(--trek-orange);
  color: var(--trek-orange);
  background: rgba(255,171,64,0.08);
}

.feedback.try-again {
  animation: feedbackFade 2s ease forwards;
}

@keyframes feedbackFade {
  0% { opacity: 0; transform: translateY(-6px); }
  15% { opacity: 1; transform: translateY(0); }
  80% { opacity: 1; }
  100% { opacity: 0; }
}

/* ══════════════════════════════════════════
   CLICKABLE SLIDE COUNTER (slide-index trigger)
   ══════════════════════════════════════════ */

.counter-clickable {
  cursor: pointer;
  position: relative;
  padding-right: 18px;
  transition: color 0.15s ease;
}

.counter-clickable::after {
  content: "\25BE";
  position: absolute;
  right: 4px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 0.85em;
  opacity: 0.75;
}

.counter-clickable:hover {
  color: var(--trek-gold);
}

.counter-clickable:focus-visible {
  outline: 2px solid var(--trek-gold);
  outline-offset: 3px;
}

/* ══════════════════════════════════════════
   SLIDE INDEX PANEL / OVERLAY
   ══════════════════════════════════════════ */

.slide-index-overlay {
  position: fixed;
  inset: 0;
  background: rgba(5, 10, 22, 0.75);
  backdrop-filter: blur(6px);
  -webkit-backdrop-filter: blur(6px);
  z-index: 9000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  animation: overlayIn 0.18s ease;
}

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

.slide-index-panel {
  background: var(--bg-panel);
  border: 1px solid var(--border-glow);
  border-radius: var(--radius-lg);
  box-shadow: 0 16px 64px rgba(0,0,0,0.6), 0 0 24px rgba(79,195,247,0.2);
  width: min(600px, 92vw);
  max-height: 85vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: panelIn 0.22s ease;
}

@keyframes panelIn {
  from { opacity: 0; transform: translateY(12px) scale(0.98); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

.slide-index-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border-subtle);
  background: linear-gradient(90deg, rgba(79,195,247,0.12), transparent);
}

.slide-index-title {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 16px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--trek-blue);
}

.slide-index-close {
  background: transparent;
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  width: 32px;
  height: 32px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  transition: all 0.15s ease;
}

.slide-index-close:hover {
  background: rgba(255,82,82,0.12);
  border-color: var(--trek-red);
  color: var(--trek-red);
}

.slide-index-list {
  overflow-y: auto;
  padding: 8px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.slide-index-row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  background: transparent;
  border: 1px solid transparent;
  border-left: 3px solid transparent;
  border-radius: 6px;
  color: var(--text-primary);
  font-family: var(--font-body);
  font-size: 14px;
  text-align: left;
  cursor: pointer;
  transition: all 0.12s ease;
  width: 100%;
}

.slide-index-row:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-subtle);
}

.slide-index-row.current {
  border-left-color: var(--trek-gold);
  background: rgba(240,165,0,0.08);
}

.slide-index-row .idx-icon {
  font-family: var(--font-mono);
  color: var(--trek-blue);
  width: 18px;
  flex-shrink: 0;
  text-align: center;
}

.slide-index-row .idx-num {
  font-family: var(--font-mono);
  color: var(--text-dim);
  font-size: 12px;
  width: 28px;
  flex-shrink: 0;
}

.slide-index-row .idx-title {
  flex: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.slide-index-row.current .idx-title {
  font-weight: 700;
  color: var(--trek-gold);
}

.slide-index-row .idx-status {
  font-family: var(--font-mono);
  font-size: 14px;
  width: 18px;
  flex-shrink: 0;
  text-align: center;
}

.slide-index-row .idx-status.ok { color: var(--trek-green); }
.slide-index-row .idx-status.bad { color: var(--trek-red); }
.slide-index-row .idx-status.empty { color: var(--text-dim); }

@media (max-width: 640px) {
  .slide-index-overlay {
    padding: 0;
    align-items: stretch;
  }
  .slide-index-panel {
    width: 100%;
    max-height: 100%;
    border-radius: 0;
  }
}

/* ══════════════════════════════════════════
   CHALLENGE SLIDE (FRQ-style, multi-part)
   ══════════════════════════════════════════ */

.slide-badge.badge-challenge,
.badge.badge-challenge {
  background: linear-gradient(135deg, rgba(255,171,64,0.18), rgba(179,136,255,0.14));
  border-color: rgba(255,171,64,0.45);
  color: var(--trek-orange);
}

.challenge-card {
  margin-top: 12px;
  padding: 18px;
  border: 1px solid rgba(255,171,64,0.3);
  border-radius: var(--radius);
  background: linear-gradient(180deg, rgba(255,171,64,0.05), transparent);
  box-shadow: inset 0 0 24px rgba(255,171,64,0.04);
}

.challenge-scenario {
  color: var(--text-primary);
  margin-bottom: 16px;
  padding-bottom: 16px;
  border-bottom: 1px dashed rgba(255,171,64,0.25);
}

.challenge-parts {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.challenge-part {
  padding: 16px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
}

.challenge-part-header {
  display: flex;
  gap: 10px;
  margin-bottom: 12px;
  align-items: baseline;
  flex-wrap: wrap;
}

.challenge-part .part-label {
  font-family: var(--font-display);
  font-weight: 700;
  color: var(--trek-orange);
  font-size: 15px;
  min-width: 28px;
}

.challenge-part .part-prompt {
  color: var(--text-primary);
  flex: 1;
  line-height: 1.55;
}

.frq-text-area {
  width: 100%;
  min-height: 110px;
  padding: 12px 14px;
  background: var(--bg-deep);
  border: 1px solid var(--border-subtle);
  border-radius: 6px;
  color: var(--text-primary);
  font-family: var(--font-body);
  font-size: 14px;
  line-height: 1.55;
  resize: vertical;
}

.frq-text-area:focus {
  outline: none;
  border-color: var(--trek-blue);
  box-shadow: 0 0 0 2px rgba(79,195,247,0.2);
}

.sample-response-box {
  margin-top: 12px;
  padding: 14px 16px;
  background: rgba(179,136,255,0.08);
  border: 1px solid rgba(179,136,255,0.3);
  border-radius: var(--radius);
}

.sample-response-box .sample-label,
.sample-response-box .rubric-label {
  font-family: var(--font-display);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  font-size: 11px;
  font-weight: 700;
  color: var(--trek-purple);
  margin-bottom: 6px;
}

.sample-response-box .rubric-label { margin-top: 12px; }

.sample-response-box .sample-body {
  color: var(--text-primary);
  font-size: 14px;
  line-height: 1.6;
}

.sample-response-box .rubric-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.sample-response-box .rubric-list li {
  padding: 4px 0 4px 16px;
  position: relative;
  font-size: 13px;
  color: var(--text-secondary);
}

.sample-response-box .rubric-list li::before {
  content: "\2713";
  position: absolute;
  left: 0;
  color: var(--trek-green);
}

.challenge-part .btn-row {
  margin-top: 12px;
}