/* ========================================
   PROSTHETICS LEARNING SITE - STYLES
   Sports-themed educational site for 4th graders
   ======================================== */

/* --- CSS Custom Properties --- */
:root {
  /* Primary palette - energetic sports vibes */
  --color-primary: #0055ff;
  --color-primary-dark: #0044cc;
  --color-primary-light: #e8f0ff;
  --color-accent: #ff6b00;
  --color-accent-dark: #e55f00;
  --color-accent-light: #fff3e8;
  --color-secondary: #00c853;
  --color-secondary-dark: #00a844;
  --color-secondary-light: #e8faf0;
  --color-highlight: #ff2d55;
  --color-highlight-light: #fff0f3;
  --color-purple: #7c3aed;
  --color-purple-light: #f3eeff;
  --color-cyan: #06b6d4;
  --color-cyan-light: #e8fafe;

  /* Neutrals */
  --color-bg: #f8f9fc;
  --color-surface: #ffffff;
  --color-text: #1a1a2e;
  --color-text-secondary: #4a5568;
  --color-text-light: #718096;
  --color-border: #e2e8f0;
  --color-border-light: #edf2f7;

  /* Status */
  --color-success: #10b981;
  --color-success-bg: #ecfdf5;
  --color-error: #ef4444;
  --color-error-bg: #fef2f2;
  --color-warning: #f59e0b;
  --color-warning-bg: #fffbeb;

  /* Typography */
  --font-body: 'Segoe UI', system-ui, -apple-system, sans-serif;
  --font-heading: 'Segoe UI', system-ui, -apple-system, sans-serif;
  --font-size-sm: 0.875rem;
  --font-size-base: 1.125rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: 1.5rem;
  --font-size-2xl: 2rem;
  --font-size-3xl: 2.5rem;
  --font-size-4xl: 3.5rem;

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;

  /* Borders & Shadows */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.12);
  --shadow-xl: 0 12px 40px rgba(0, 0, 0, 0.15);
  --shadow-glow: 0 0 20px rgba(0, 85, 255, 0.15);

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;

  /* Layout */
  --max-width: 1200px;
  --content-width: 800px;
  --nav-height: 64px;
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: var(--font-size-base);
  line-height: 1.7;
  color: var(--color-text);
  background: var(--color-bg);
  min-height: 100vh;
  overflow-x: hidden;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary-dark);
}

button {
  cursor: pointer;
  font-family: inherit;
  font-size: inherit;
  border: none;
  background: none;
}

/* --- Typography --- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 800;
  line-height: 1.2;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

h1 { font-size: var(--font-size-4xl); }
h2 { font-size: var(--font-size-3xl); }
h3 { font-size: var(--font-size-2xl); }
h4 { font-size: var(--font-size-xl); }

p {
  margin-bottom: var(--space-md);
  max-width: 65ch;
}

strong {
  font-weight: 700;
  color: var(--color-text);
}

/* --- Skip Link (Accessibility) --- */
.skip-link {
  position: absolute;
  top: -100%;
  left: var(--space-md);
  padding: var(--space-sm) var(--space-md);
  background: var(--color-primary);
  color: #fff;
  border-radius: var(--radius-sm);
  z-index: 1000;
  font-weight: 600;
}

.skip-link:focus {
  top: var(--space-md);
  color: #fff;
}

/* --- Navigation Bar --- */
.site-nav {
  position: sticky;
  top: 0;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border-light);
  z-index: 100;
  height: var(--nav-height);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl);
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 800;
  font-size: var(--font-size-lg);
  color: var(--color-text);
}

.nav-brand .brand-icon {
  font-size: 1.5rem;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
  list-style: none;
}

.nav-links a {
  font-weight: 600;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-primary);
  background: var(--color-primary-light);
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: var(--space-sm);
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  border-radius: 2px;
  transition: all var(--transition-fast);
}

/* --- Hero Section --- */
.hero {
  background: linear-gradient(135deg, #0044cc 0%, #0066ff 40%, #4d94ff 100%);
  color: #fff;
  padding: var(--space-3xl) var(--space-xl);
  text-align: center;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 50%, rgba(255, 255, 255, 0.08) 0%, transparent 50%),
              radial-gradient(circle at 70% 80%, rgba(255, 107, 0, 0.1) 0%, transparent 50%);
  animation: heroShimmer 8s ease-in-out infinite alternate;
}

@keyframes heroShimmer {
  from { transform: rotate(0deg); }
  to { transform: rotate(3deg); }
}

.hero-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

.hero h1 {
  color: #fff;
  margin-bottom: var(--space-lg);
  font-size: clamp(2rem, 5vw, 3.5rem);
}

.hero h1 .highlight {
  color: var(--color-accent);
  display: inline-block;
}

.hero-subtitle {
  font-size: var(--font-size-xl);
  opacity: 0.9;
  max-width: 700px;
  margin: 0 auto var(--space-2xl);
  line-height: 1.6;
}

/* --- Brain Visualization (Homepage) --- */
.brain-viz {
  background: rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-xl);
  padding: var(--space-2xl);
  margin: var(--space-2xl) auto;
  max-width: 700px;
  backdrop-filter: blur(8px);
  border: 1px solid rgba(255, 255, 255, 0.15);
}

.brain-viz-title {
  font-size: var(--font-size-lg);
  font-weight: 700;
  margin-bottom: var(--space-lg);
  color: #fff;
}

.signal-path {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.signal-node {
  background: rgba(255, 255, 255, 0.15);
  border: 2px solid rgba(255, 255, 255, 0.3);
  border-radius: var(--radius-md);
  padding: var(--space-md) var(--space-lg);
  text-align: center;
  cursor: pointer;
  transition: all var(--transition-base);
  min-width: 100px;
}

.signal-node:hover,
.signal-node.active {
  background: rgba(255, 255, 255, 0.25);
  border-color: var(--color-accent);
  transform: scale(1.05);
}

.signal-node .node-icon {
  font-size: 2rem;
  margin-bottom: var(--space-xs);
  display: block;
}

.signal-node .node-label {
  font-size: var(--font-size-sm);
  font-weight: 600;
}

.signal-arrow {
  font-size: 1.5rem;
  opacity: 0.5;
  transition: opacity var(--transition-base);
}

.signal-arrow.active {
  opacity: 1;
  color: var(--color-accent);
  animation: pulseArrow 0.6s ease;
}

@keyframes pulseArrow {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.3); }
}

.viz-instruction {
  margin-top: var(--space-lg);
  font-size: var(--font-size-sm);
  opacity: 0.7;
}

/* --- Section Cards Grid --- */
.sections-grid {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-3xl) var(--space-xl);
}

.sections-grid .grid-title {
  text-align: center;
  margin-bottom: var(--space-2xl);
}

.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--space-xl);
}

.section-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  box-shadow: var(--shadow-sm);
  border: 2px solid var(--color-border-light);
  transition: all var(--transition-base);
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
}

.section-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--card-accent, var(--color-primary));
}

.section-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--card-accent, var(--color-primary));
}

.section-card .card-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.section-card h3 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--space-sm);
}

.section-card p {
  color: var(--color-text-secondary);
  font-size: var(--font-size-base);
  flex-grow: 1;
  margin-bottom: var(--space-lg);
}

.section-card .card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.card-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 700;
  color: var(--card-accent, var(--color-primary));
  transition: gap var(--transition-fast);
}

.card-link:hover {
  gap: var(--space-md);
  color: var(--card-accent, var(--color-primary));
}

.card-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  font-size: var(--font-size-sm);
  font-weight: 600;
  padding: var(--space-xs) var(--space-sm);
  border-radius: 100px;
  background: var(--color-success-bg);
  color: var(--color-success);
}

.card-badge.incomplete {
  background: var(--color-border-light);
  color: var(--color-text-light);
}

/* Card accent colors */
.section-card[data-section="body"] { --card-accent: var(--color-primary); }
.section-card[data-section="mechanical"] { --card-accent: var(--color-accent); }
.section-card[data-section="blades"] { --card-accent: var(--color-secondary); }
.section-card[data-section="bionic"] { --card-accent: var(--color-purple); }
.section-card[data-section="athletes"] { --card-accent: var(--color-highlight); }
.section-card[data-section="future"] { --card-accent: var(--color-cyan); }

/* --- Progress Tracker --- */
.progress-section {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl) var(--space-3xl);
}

.progress-bar-container {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-xl) var(--space-2xl);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
}

.progress-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-md);
}

.progress-header h3 {
  font-size: var(--font-size-lg);
}

.progress-count {
  font-weight: 700;
  color: var(--color-primary);
}

.progress-track {
  width: 100%;
  height: 12px;
  background: var(--color-border-light);
  border-radius: 100px;
  overflow: hidden;
  margin-bottom: var(--space-lg);
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  border-radius: 100px;
  transition: width var(--transition-slow);
  width: 0%;
}

.progress-dots {
  display: flex;
  justify-content: space-between;
  gap: var(--space-sm);
}

.progress-dot {
  flex: 1;
  text-align: center;
}

.progress-dot .dot {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-border-light);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-sm);
  font-weight: 700;
  margin-bottom: var(--space-xs);
  transition: all var(--transition-base);
  color: var(--color-text-light);
}

.progress-dot.completed .dot {
  background: var(--color-success);
  color: #fff;
}

.progress-dot.current .dot {
  background: var(--color-primary);
  color: #fff;
  box-shadow: 0 0 0 4px var(--color-primary-light);
}

.progress-dot .dot-label {
  font-size: 0.75rem;
  color: var(--color-text-light);
  display: block;
}

/* --- Videos Button (Homepage) --- */
.videos-cta {
  text-align: center;
  padding: var(--space-2xl) var(--space-xl) var(--space-3xl);
}

.btn-videos {
  display: inline-flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-lg) var(--space-2xl);
  background: linear-gradient(135deg, var(--color-highlight) 0%, #ff6090 100%);
  color: #fff;
  font-size: var(--font-size-xl);
  font-weight: 800;
  border-radius: var(--radius-xl);
  box-shadow: 0 4px 20px rgba(255, 45, 85, 0.3);
  transition: all var(--transition-base);
}

.btn-videos:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 30px rgba(255, 45, 85, 0.4);
  color: #fff;
}

.btn-videos .btn-icon {
  font-size: 1.5rem;
}

/* --- Achievement Badges Section --- */
.badges-section {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl) var(--space-3xl);
}

.badges-container {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border-light);
}

.badges-grid {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-lg);
  justify-content: center;
}

.badge-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-sm);
  width: 100px;
  text-align: center;
}

.badge-icon {
  width: 64px;
  height: 64px;
  border-radius: 50%;
  background: var(--color-border-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.8rem;
  transition: all var(--transition-base);
  filter: grayscale(1);
  opacity: 0.4;
}

.badge-item.earned .badge-icon {
  background: var(--color-warning-bg);
  filter: none;
  opacity: 1;
  box-shadow: 0 0 0 3px var(--color-warning), 0 4px 15px rgba(245, 158, 11, 0.3);
}

.badge-item .badge-label {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-text-light);
}

.badge-item.earned .badge-label {
  color: var(--color-text);
}

/* --- Content Page Layout --- */
.page-header {
  background: linear-gradient(135deg, var(--page-color, var(--color-primary)) 0%, var(--page-color-end, #4d94ff) 100%);
  color: #fff;
  padding: var(--space-2xl) var(--space-xl);
  position: relative;
}

.page-header-inner {
  max-width: var(--content-width);
  margin: 0 auto;
}

.page-nav-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-xl);
}

.btn-back {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  color: rgba(255, 255, 255, 0.8);
  font-weight: 600;
  font-size: var(--font-size-sm);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}

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

.section-indicator {
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: rgba(255, 255, 255, 0.8);
  background: rgba(255, 255, 255, 0.15);
  padding: var(--space-xs) var(--space-md);
  border-radius: 100px;
}

.page-header h1 {
  color: #fff;
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  margin-bottom: var(--space-sm);
}

.page-header .page-description {
  font-size: var(--font-size-lg);
  opacity: 0.9;
  max-width: 600px;
}

/* --- Content Area --- */
.content-area {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: var(--space-2xl) var(--space-xl);
}

.content-section {
  margin-bottom: var(--space-3xl);
}

.content-section h2 {
  font-size: var(--font-size-2xl);
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-sm);
  border-bottom: 3px solid var(--page-color, var(--color-primary));
  display: inline-block;
}

.content-section h3 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--space-md);
  margin-top: var(--space-xl);
}

/* --- Did You Know Box --- */
.did-you-know {
  background: var(--color-accent-light);
  border-left: 4px solid var(--color-accent);
  border-radius: var(--radius-md);
  padding: var(--space-lg) var(--space-xl);
  margin: var(--space-xl) 0;
}

.did-you-know .dyk-header {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 800;
  color: var(--color-accent);
  margin-bottom: var(--space-sm);
  font-size: var(--font-size-lg);
}

.did-you-know p {
  color: var(--color-text);
  margin-bottom: 0;
}

/* --- Key Stat Callout --- */
.stat-callout {
  background: linear-gradient(135deg, var(--color-primary) 0%, #4d94ff 100%);
  color: #fff;
  border-radius: var(--radius-lg);
  padding: var(--space-xl) var(--space-2xl);
  text-align: center;
  margin: var(--space-xl) 0;
}

.stat-callout .stat-number {
  font-size: var(--font-size-4xl);
  font-weight: 900;
  display: block;
  line-height: 1;
  margin-bottom: var(--space-sm);
}

.stat-callout .stat-label {
  font-size: var(--font-size-lg);
  opacity: 0.9;
}

/* --- Interactive Diagram --- */
.interactive-diagram {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  margin: var(--space-xl) 0;
  text-align: center;
}

.interactive-diagram .diagram-title {
  font-size: var(--font-size-lg);
  font-weight: 700;
  margin-bottom: var(--space-lg);
}

.diagram-instruction {
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  margin-top: var(--space-md);
}

/* --- Image Placeholder --- */
.image-placeholder {
  background: var(--color-border-light);
  border: 2px dashed var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-2xl);
  text-align: center;
  margin: var(--space-xl) 0;
  min-height: 200px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
}

.image-placeholder .placeholder-icon {
  font-size: 3rem;
  opacity: 0.4;
}

.image-placeholder .placeholder-text {
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  font-style: italic;
}

/* --- Comparison Cards --- */
.comparison {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: var(--space-lg);
  align-items: start;
  margin: var(--space-xl) 0;
}

.comparison-item {
  background: var(--color-surface);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  border: 2px solid var(--color-border-light);
  text-align: center;
}

.comparison-item h4 {
  margin-bottom: var(--space-sm);
}

.comparison-vs {
  display: flex;
  align-items: center;
  font-weight: 900;
  font-size: var(--font-size-xl);
  color: var(--color-accent);
}

/* --- Interactive Try It Element --- */
.try-it-box {
  background: linear-gradient(135deg, var(--color-purple-light) 0%, var(--color-primary-light) 100%);
  border: 2px solid var(--color-purple);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  margin: var(--space-xl) 0;
  text-align: center;
}

.try-it-box .try-it-label {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  background: var(--color-purple);
  color: #fff;
  padding: var(--space-xs) var(--space-md);
  border-radius: 100px;
  font-weight: 700;
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-md);
}

.try-it-box .try-it-content {
  font-size: var(--font-size-lg);
  margin-bottom: var(--space-lg);
}

/* --- Interactive Buttons --- */
.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  background: var(--color-primary);
  color: #fff;
  font-weight: 700;
  font-size: var(--font-size-base);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
  box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
  background: var(--color-primary-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: #fff;
}

.btn-accent {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  background: var(--color-accent);
  color: #fff;
  font-weight: 700;
  font-size: var(--font-size-base);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
  box-shadow: var(--shadow-sm);
}

.btn-accent:hover {
  background: var(--color-accent-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: #fff;
}

.btn-success {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  background: var(--color-success);
  color: #fff;
  font-weight: 700;
  font-size: var(--font-size-base);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
}

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

.btn-outline {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  background: transparent;
  color: var(--color-text);
  font-weight: 700;
  font-size: var(--font-size-base);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
}

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

/* --- Quiz Section --- */
.quiz-section {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  margin: var(--space-3xl) 0;
  box-shadow: var(--shadow-md);
  border: 2px solid var(--color-border-light);
}

.quiz-section .quiz-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.quiz-section .quiz-header h3 {
  margin-bottom: 0;
}

.quiz-question {
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-xl);
  border-bottom: 1px solid var(--color-border-light);
}

.quiz-question:last-of-type {
  border-bottom: none;
  margin-bottom: var(--space-lg);
}

.quiz-question .q-text {
  font-weight: 700;
  font-size: var(--font-size-lg);
  margin-bottom: var(--space-md);
}

.quiz-question .q-number {
  color: var(--color-primary);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
}

.quiz-option {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-weight: 500;
}

.quiz-option:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.quiz-option.correct {
  border-color: var(--color-success);
  background: var(--color-success-bg);
  color: var(--color-success);
}

.quiz-option.incorrect {
  border-color: var(--color-error);
  background: var(--color-error-bg);
  color: var(--color-error);
}

.quiz-option.disabled {
  pointer-events: none;
  opacity: 0.6;
}

.quiz-option .option-marker {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-border-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: var(--font-size-sm);
  flex-shrink: 0;
}

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

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

.quiz-feedback {
  margin-top: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: var(--font-size-sm);
  display: none;
}

.quiz-feedback.show {
  display: block;
}

.quiz-feedback.correct {
  background: var(--color-success-bg);
  color: var(--color-success);
}

.quiz-feedback.incorrect {
  background: var(--color-error-bg);
  color: var(--color-error);
}

.quiz-score {
  text-align: center;
  padding: var(--space-lg);
  background: var(--color-primary-light);
  border-radius: var(--radius-md);
  display: none;
}

.quiz-score.show {
  display: block;
}

.quiz-score .score-text {
  font-size: var(--font-size-xl);
  font-weight: 800;
  color: var(--color-primary);
}

/* --- Mark Complete Button --- */
.complete-section {
  text-align: center;
  padding: var(--space-2xl) 0;
  margin-top: var(--space-xl);
  border-top: 2px solid var(--color-border-light);
}

.btn-complete {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-lg) var(--space-2xl);
  background: var(--color-success);
  color: #fff;
  font-size: var(--font-size-lg);
  font-weight: 800;
  border-radius: var(--radius-xl);
  transition: all var(--transition-base);
  box-shadow: 0 4px 15px rgba(16, 185, 129, 0.3);
}

.btn-complete:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgba(16, 185, 129, 0.4);
  color: #fff;
}

.btn-complete.completed {
  background: var(--color-border);
  box-shadow: none;
  cursor: default;
}

.btn-complete.completed:hover {
  transform: none;
}

/* --- Page Navigation (prev/next) --- */
.page-nav-bottom {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-2xl) var(--space-xl);
  max-width: var(--content-width);
  margin: 0 auto;
  gap: var(--space-lg);
}

.nav-arrow {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-weight: 700;
  color: var(--color-text);
  transition: all var(--transition-fast);
  text-align: left;
}

.nav-arrow:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.nav-arrow .arrow-label {
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  display: block;
}

.nav-arrow .arrow-title {
  font-size: var(--font-size-base);
}

.nav-arrow.next {
  text-align: right;
}

/* --- Advanced Info Toggle --- */
.advanced-toggle {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin: var(--space-lg) 0;
  padding: var(--space-md) var(--space-lg);
  background: var(--color-cyan-light);
  border: 2px solid var(--color-cyan);
  border-radius: var(--radius-md);
  cursor: pointer;
  font-weight: 700;
  color: var(--color-cyan);
  transition: all var(--transition-fast);
}

.advanced-toggle:hover {
  background: #d5f5fa;
}

.advanced-content {
  display: none;
  padding: var(--space-lg);
  background: var(--color-cyan-light);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-lg);
  border: 1px solid var(--color-cyan);
}

.advanced-content.show {
  display: block;
  animation: slideDown 0.3s ease;
}

@keyframes slideDown {
  from { opacity: 0; transform: translateY(-8px); }
  to { opacity: 1; transform: translateY(0); }
}

/* --- Athlete Profile Cards --- */
.athlete-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--space-xl);
  margin: var(--space-xl) 0;
}

.athlete-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 2px solid var(--color-border-light);
  transition: all var(--transition-base);
}

.athlete-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.athlete-photo {
  background: linear-gradient(135deg, var(--color-primary-light) 0%, var(--color-purple-light) 100%);
  height: 180px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 4rem;
}

.athlete-info {
  padding: var(--space-lg);
}

.athlete-info h3 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--space-xs);
}

.athlete-sport {
  font-weight: 600;
  color: var(--color-primary);
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-sm);
}

.athlete-achievement {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-md);
}

.athlete-medals {
  display: flex;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
}

.medal {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  padding: 2px 8px;
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 700;
}

.medal.gold {
  background: #fef3c7;
  color: #92400e;
}

.medal.silver {
  background: #f1f5f9;
  color: #475569;
}

.medal.bronze {
  background: #fed7aa;
  color: #9a3412;
}

.athlete-expandable {
  display: none;
  padding: var(--space-md);
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  margin-top: var(--space-md);
  font-size: var(--font-size-sm);
}

.athlete-expandable.show {
  display: block;
  animation: slideDown 0.3s ease;
}

.btn-learn-more {
  font-weight: 700;
  color: var(--color-primary);
  font-size: var(--font-size-sm);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
}

/* --- Future Tech Cards --- */
.innovation-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: var(--space-xl);
  margin: var(--space-xl) 0;
}

.innovation-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  box-shadow: var(--shadow-sm);
  border: 2px solid var(--color-border-light);
  transition: all var(--transition-base);
}

.innovation-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.innovation-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.innovation-card h3 {
  font-size: var(--font-size-lg);
  margin-bottom: var(--space-sm);
}

/* --- Design Your Own Prosthetic --- */
.customizer {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  margin: var(--space-2xl) 0;
}

.customizer h3 {
  text-align: center;
  margin-bottom: var(--space-xl);
}

.customizer-options {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: var(--space-lg);
  margin-bottom: var(--space-xl);
}

.customizer-group label {
  display: block;
  font-weight: 700;
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-sm);
}

.customizer-group select {
  width: 100%;
  padding: var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-size: var(--font-size-base);
  font-family: inherit;
  background: var(--color-surface);
  cursor: pointer;
}

.customizer-group select:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-light);
}

.customizer-preview {
  text-align: center;
  padding: var(--space-2xl);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  min-height: 200px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-xl);
}

.customizer-preview .preview-icon {
  font-size: 4rem;
  margin-bottom: var(--space-md);
}

/* --- Videos Page --- */
.video-categories {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
  margin-bottom: var(--space-xl);
}

.video-category-btn {
  padding: var(--space-sm) var(--space-lg);
  border: 2px solid var(--color-border);
  border-radius: 100px;
  font-weight: 700;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
  cursor: pointer;
}

.video-category-btn:hover,
.video-category-btn.active {
  border-color: var(--color-primary);
  background: var(--color-primary);
  color: #fff;
}

.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--space-xl);
}

.video-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 2px solid var(--color-border-light);
  transition: all var(--transition-base);
}

.video-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.video-thumbnail {
  background: linear-gradient(135deg, #1a1a2e 0%, #2d2d5e 100%);
  height: 200px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}

.video-play-btn {
  width: 60px;
  height: 60px;
  background: rgba(255, 255, 255, 0.9);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  transition: all var(--transition-fast);
}

.video-card:hover .video-play-btn {
  transform: scale(1.1);
  background: #fff;
}

.video-duration {
  position: absolute;
  bottom: 8px;
  right: 8px;
  background: rgba(0, 0, 0, 0.7);
  color: #fff;
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 0.75rem;
  font-weight: 600;
}

.video-info {
  padding: var(--space-lg);
}

.video-info h3 {
  font-size: var(--font-size-base);
  margin-bottom: var(--space-sm);
}

.video-info p {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}

.video-tag {
  display: inline-block;
  padding: 2px 8px;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 600;
}

/* --- Bookmark Button --- */
.btn-bookmark {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  padding: var(--space-sm) var(--space-md);
  background: transparent;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.btn-bookmark:hover {
  border-color: var(--color-warning);
  color: var(--color-warning);
}

.btn-bookmark.saved {
  background: var(--color-warning-bg);
  border-color: var(--color-warning);
  color: var(--color-warning);
}

/* --- Print Button --- */
.btn-print {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: transparent;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.btn-print:hover {
  border-color: var(--color-text);
  color: var(--color-text);
}

/* --- Page Tools Bar --- */
.page-tools {
  display: flex;
  justify-content: flex-end;
  gap: var(--space-sm);
  margin-bottom: var(--space-xl);
}

/* --- Flowchart --- */
.flowchart {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-sm);
  margin: var(--space-xl) 0;
}

.flowchart-step {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-md) var(--space-xl);
  font-weight: 700;
  text-align: center;
  max-width: 300px;
  width: 100%;
  transition: all var(--transition-base);
  cursor: pointer;
}

.flowchart-step:hover,
.flowchart-step.active {
  border-color: var(--color-purple);
  background: var(--color-purple-light);
  transform: scale(1.03);
}

.flowchart-arrow {
  font-size: 1.5rem;
  color: var(--color-text-light);
}

/* --- Grip Patterns Grid --- */
.grip-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: var(--space-md);
  margin: var(--space-xl) 0;
}

.grip-item {
  background: var(--color-surface);
  border: 2px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  text-align: center;
  cursor: pointer;
  transition: all var(--transition-base);
}

.grip-item:hover,
.grip-item.active {
  border-color: var(--color-purple);
  background: var(--color-purple-light);
  transform: scale(1.05);
}

.grip-item .grip-icon {
  font-size: 2rem;
  margin-bottom: var(--space-sm);
  display: block;
}

.grip-item .grip-name {
  font-size: var(--font-size-sm);
  font-weight: 700;
}

/* --- Price Comparison --- */
.price-comparison {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-xl);
  margin: var(--space-xl) 0;
}

.price-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  text-align: center;
  border: 2px solid var(--color-border-light);
}

.price-card .price-amount {
  font-size: var(--font-size-3xl);
  font-weight: 900;
  color: var(--color-text);
  margin: var(--space-md) 0;
}

.price-card .price-label {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

.price-card.highlight {
  border-color: var(--color-success);
  background: var(--color-success-bg);
}

.price-card.highlight .price-amount {
  color: var(--color-success);
}

/* --- Footer --- */
.site-footer {
  background: var(--color-text);
  color: rgba(255, 255, 255, 0.7);
  padding: var(--space-2xl) var(--space-xl);
  text-align: center;
  margin-top: var(--space-3xl);
}

.site-footer p {
  max-width: none;
  margin-bottom: var(--space-sm);
  font-size: var(--font-size-sm);
}

.site-footer a {
  color: rgba(255, 255, 255, 0.9);
}

/* --- Badge Notification --- */
.badge-notification {
  position: fixed;
  top: calc(var(--nav-height) + var(--space-md));
  right: var(--space-xl);
  background: var(--color-surface);
  border: 2px solid var(--color-warning);
  border-radius: var(--radius-lg);
  padding: var(--space-lg) var(--space-xl);
  box-shadow: var(--shadow-xl);
  z-index: 200;
  display: flex;
  align-items: center;
  gap: var(--space-md);
  transform: translateX(120%);
  transition: transform var(--transition-slow);
}

.badge-notification.show {
  transform: translateX(0);
}

.badge-notification .notif-icon {
  font-size: 2rem;
}

.badge-notification .notif-text {
  font-weight: 700;
}

.badge-notification .notif-subtext {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

/* --- Responsive Design --- */
@media (max-width: 768px) {
  :root {
    --font-size-base: 1rem;
    --font-size-4xl: 2.25rem;
    --font-size-3xl: 1.75rem;
    --font-size-2xl: 1.5rem;
  }

  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-surface);
    flex-direction: column;
    padding: var(--space-lg);
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-lg);
  }

  .nav-links.open {
    display: flex;
  }

  .nav-toggle {
    display: flex;
  }

  .hero {
    padding: var(--space-2xl) var(--space-md);
  }

  .cards-grid {
    grid-template-columns: 1fr;
  }

  .comparison {
    grid-template-columns: 1fr;
  }

  .comparison-vs {
    justify-content: center;
  }

  .page-nav-bottom {
    flex-direction: column;
  }

  .nav-arrow {
    width: 100%;
    justify-content: center;
    text-align: center;
  }

  .progress-dots {
    flex-wrap: wrap;
  }

  .athlete-grid {
    grid-template-columns: 1fr;
  }

  .video-grid {
    grid-template-columns: 1fr;
  }

  .price-comparison {
    grid-template-columns: 1fr;
  }

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

  .badge-notification {
    left: var(--space-md);
    right: var(--space-md);
    top: auto;
    bottom: var(--space-md);
    transform: translateY(120%);
  }

  .badge-notification.show {
    transform: translateY(0);
  }

  .signal-path {
    flex-direction: column;
  }

  .signal-arrow {
    transform: rotate(90deg);
  }
}

@media (max-width: 480px) {
  .grip-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .badges-grid {
    gap: var(--space-md);
  }

  .badge-item {
    width: 80px;
  }

  .innovation-grid {
    grid-template-columns: 1fr;
  }
}

/* --- Print Styles --- */
@media print {
  .site-nav,
  .btn-complete,
  .btn-bookmark,
  .btn-print,
  .page-nav-bottom,
  .quiz-section,
  .try-it-box,
  .page-tools,
  .videos-cta,
  .badge-notification,
  .nav-toggle {
    display: none !important;
  }

  body {
    background: #fff;
    color: #000;
    font-size: 12pt;
  }

  .page-header {
    background: none !important;
    color: #000 !important;
    padding: 0 0 1em;
    border-bottom: 2px solid #000;
  }

  .page-header h1,
  .page-header .page-description {
    color: #000 !important;
  }

  .content-area {
    padding: 1em 0;
  }

  .did-you-know {
    border: 1px solid #999;
    background: #f5f5f5;
  }

  .stat-callout {
    background: #f5f5f5 !important;
    color: #000 !important;
    border: 1px solid #999;
  }

  .stat-callout .stat-number,
  .stat-callout .stat-label {
    color: #000 !important;
  }
}

/* --- Focus Styles (Accessibility) --- */
:focus-visible {
  outline: 3px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: 2px;
}

button:focus-visible,
a:focus-visible {
  outline: 3px solid var(--color-primary);
  outline-offset: 2px;
}

/* --- Reading Level Toggle --- */
.reading-toggle {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-xl);
  border: 1px solid var(--color-border-light);
}

.reading-toggle .toggle-label {
  font-weight: 700;
  font-size: var(--font-size-sm);
}

.toggle-switch {
  position: relative;
  width: 48px;
  height: 26px;
  background: var(--color-border);
  border-radius: 100px;
  cursor: pointer;
  transition: background var(--transition-fast);
}

.toggle-switch.on {
  background: var(--color-cyan);
}

.toggle-switch .toggle-knob {
  position: absolute;
  top: 3px;
  left: 3px;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 50%;
  transition: transform var(--transition-fast);
  box-shadow: var(--shadow-sm);
}

.toggle-switch.on .toggle-knob {
  transform: translateX(22px);
}

/* --- Spring Animation for Running Blades --- */
.spring-demo {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-md);
  margin: var(--space-xl) 0;
  padding: var(--space-2xl);
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
}

.spring-visual {
  width: 120px;
  height: 200px;
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-end;
}

.spring-blade {
  width: 40px;
  height: 160px;
  background: linear-gradient(180deg, #333 0%, #666 100%);
  border-radius: 0 0 40px 4px;
  transform-origin: top center;
  transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.spring-blade.compressed {
  transform: scaleY(0.7) scaleX(1.2);
}

.spring-label {
  font-weight: 700;
  font-size: var(--font-size-lg);
  text-align: center;
}

/* --- Utility Classes --- */
.text-center { text-align: center; }
.mt-sm { margin-top: var(--space-sm); }
.mt-md { margin-top: var(--space-md); }
.mt-lg { margin-top: var(--space-lg); }
.mt-xl { margin-top: var(--space-xl); }
.mb-sm { margin-bottom: var(--space-sm); }
.mb-md { margin-bottom: var(--space-md); }
.mb-lg { margin-bottom: var(--space-lg); }
.mb-xl { margin-bottom: var(--space-xl); }
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}