/**
 * Social Network Analysis Educational Website - Styles
 * Modern, interactive, accessible CSS for learning microsite
 */

/* ==================== CSS Custom Properties ==================== */
:root {
  /* Primary colors */
  --primary: #4361ee;
  --primary-light: #6b8af7;
  --primary-dark: #2d46b9;

  /* Secondary & accent colors */
  --secondary: #7209b7;
  --accent: #f72585;

  /* Semantic colors */
  --success: #06d6a0;
  --warning: #ffd166;
  --danger: #ef476f;

  /* Background colors */
  --bg: #f0f2f5;
  --card-bg: #ffffff;

  /* Text colors */
  --text: #2b2d42;
  --text-light: #6c757d;
  --text-lighter: #adb5bd;

  /* Borders & shadows */
  --border: #dee2e6;
  --shadow: rgba(0, 0, 0, 0.08);
  --shadow-md: rgba(0, 0, 0, 0.12);
  --shadow-lg: rgba(0, 0, 0, 0.16);

  /* Border radius */
  --radius: 12px;
  --radius-sm: 8px;
  --radius-lg: 16px;

  /* Community colors */
  --community-1: #4361ee;
  --community-2: #f72585;
  --community-3: #06d6a0;
  --community-4: #ffd166;
  --community-5: #7209b7;

  /* Fonts */
  --font: system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Cascadia Code', Consolas, monospace;

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

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font);
  background-color: var(--bg);
  color: var(--text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.2;
  color: var(--text);
  margin-bottom: 1rem;
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.75rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

p {
  margin-bottom: 1rem;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: all 0.2s ease;
}

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

code {
  font-family: var(--font-mono);
  background: rgba(0, 0, 0, 0.05);
  padding: 0.125rem 0.375rem;
  border-radius: 4px;
  font-size: 0.9em;
}

/* ==================== Navigation ==================== */
.nav {
  position: sticky;
  top: 0;
  background: var(--card-bg);
  box-shadow: 0 2px 8px var(--shadow);
  z-index: 1000;
  padding: 0 var(--spacing-xl);
  height: 60px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-brand {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary);
  text-decoration: none;
}

.nav-brand:hover {
  color: var(--primary-dark);
  text-decoration: none;
}

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

.nav-links a {
  color: var(--text);
  font-weight: 500;
  padding: 0.5rem 1rem;
  border-radius: var(--radius-sm);
  transition: all 0.2s ease;
}

.nav-links a:hover {
  background: rgba(67, 97, 238, 0.1);
  text-decoration: none;
  color: var(--primary);
}

.nav-links a.active,
.nav-links a[aria-current="page"] {
  background: var(--primary);
  color: white;
}

@media (max-width: 768px) {
  .nav {
    padding: 0 var(--spacing-md);
  }

  .nav-links {
    gap: var(--spacing-sm);
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }

  .nav-links a {
    white-space: nowrap;
    padding: 0.5rem 0.75rem;
    font-size: 0.9rem;
  }
}

/* ==================== Container & Layout ==================== */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--spacing-xl);
}

@media (max-width: 768px) {
  .container {
    padding: var(--spacing-md);
  }
}

/* ==================== Cards ==================== */
.card {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: 0 2px 8px var(--shadow);
  padding: var(--spacing-xl);
  margin-bottom: var(--spacing-lg);
  transition: all 0.3s ease;
}

.card-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-md);
  color: var(--text);
}

.card-body {
  color: var(--text);
}

.card.clickable {
  cursor: pointer;
}

.card.clickable:hover {
  box-shadow: 0 4px 16px var(--shadow-md);
  transform: translateY(-2px);
}

/* ==================== Grid Layouts ==================== */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-lg);
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-lg);
}

.grid-4 {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--spacing-lg);
}

@media (max-width: 1024px) {
  .grid-3, .grid-4 {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .grid-2, .grid-3, .grid-4 {
    grid-template-columns: 1fr;
  }
}

/* ==================== Buttons ==================== */
.btn {
  display: inline-block;
  padding: 0.5rem 1.2rem;
  border-radius: var(--radius-sm);
  border: none;
  cursor: pointer;
  font-family: var(--font);
  font-size: 1rem;
  font-weight: 600;
  text-align: center;
  transition: all 0.2s ease;
  text-decoration: none;
  user-select: none;
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover {
  background: var(--primary-dark);
  box-shadow: 0 4px 12px rgba(67, 97, 238, 0.3);
  text-decoration: none;
}

.btn-primary:active {
  transform: translateY(1px);
}

.btn-secondary {
  background: transparent;
  color: var(--primary);
  border: 2px solid var(--primary);
}

.btn-secondary:hover {
  background: rgba(67, 97, 238, 0.1);
  text-decoration: none;
}

.btn-success {
  background: var(--success);
  color: white;
}

.btn-success:hover {
  background: #05c293;
  text-decoration: none;
}

.btn-warning {
  background: var(--warning);
  color: var(--text);
}

.btn-warning:hover {
  background: #ffc34d;
  text-decoration: none;
}

.btn-sm {
  padding: 0.375rem 0.875rem;
  font-size: 0.875rem;
}

.btn-group {
  display: flex;
  gap: var(--spacing-sm);
  flex-wrap: wrap;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  pointer-events: none;
}

/* ==================== Formula Cards ==================== */
.formula-card {
  background: #f0f4ff;
  border-left: 4px solid var(--primary);
  border-radius: var(--radius-sm);
  padding: var(--spacing-lg);
  margin: var(--spacing-lg) 0;
}

.formula-label {
  font-size: 0.875rem;
  color: var(--text-light);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--spacing-sm);
  font-weight: 600;
}

.formula {
  font-family: var(--font-mono);
  font-size: 1.25rem;
  text-align: center;
  margin: var(--spacing-md) 0;
  color: var(--text);
  line-height: 1.8;
}

/* ==================== Info Panels ==================== */
.info-panel {
  background: var(--card-bg);
  border-left: 4px solid var(--primary);
  border-radius: var(--radius-sm);
  padding: var(--spacing-lg);
  margin: var(--spacing-lg) 0;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
}

.info-panel.tip {
  border-left-color: var(--success);
  background: #f0fdf9;
}

.info-panel.warning {
  border-left-color: var(--warning);
  background: #fffbf0;
}

.info-panel.concept {
  border-left-color: var(--primary);
  background: #f0f4ff;
}

.info-panel.misunderstanding {
  border-left-color: var(--accent);
  background: #fff0f6;
}

.info-panel .panel-header {
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  color: var(--text);
  font-size: 1.1rem;
}

.info-panel.misunderstanding .panel-header::before {
  content: "⚠ Common Misunderstanding: ";
  color: var(--accent);
}

/* ==================== Tables ==================== */
.data-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--card-bg);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: 0 2px 8px var(--shadow);
  margin: var(--spacing-lg) 0;
}

.data-table thead {
  position: sticky;
  top: 60px;
  background: var(--primary-dark);
  color: white;
  z-index: 10;
}

.data-table th {
  padding: 1rem;
  text-align: left;
  font-weight: 700;
  border-bottom: 2px solid var(--primary);
}

.data-table td {
  padding: 0.875rem 1rem;
  border-bottom: 1px solid var(--border);
}

.data-table tbody tr:hover {
  background: rgba(67, 97, 238, 0.05);
}

.data-table tbody tr:nth-child(even) {
  background: rgba(0, 0, 0, 0.02);
}

.data-table tbody tr:nth-child(even):hover {
  background: rgba(67, 97, 238, 0.08);
}

.positive-contribution {
  background: rgba(6, 214, 160, 0.15) !important;
}

.negative-contribution {
  background: rgba(247, 37, 133, 0.15) !important;
}

.zero-contribution {
  background: rgba(173, 181, 189, 0.1) !important;
}

/* ==================== Controls Panel ==================== */
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-md);
  align-items: center;
  padding: var(--spacing-lg);
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: 0 2px 4px var(--shadow);
  margin-bottom: var(--spacing-lg);
}

.controls label {
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--text);
  margin-right: var(--spacing-sm);
}

/* ==================== Select Dropdown ==================== */
.select, select {
  padding: 0.5rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--card-bg);
  color: var(--text);
  font-family: var(--font);
  font-size: 1rem;
  cursor: pointer;
  transition: all 0.2s ease;
}

.select:hover, select:hover {
  border-color: var(--primary-light);
}

.select:focus, select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(67, 97, 238, 0.1);
}

/* ==================== Slider ==================== */
.slider-container {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  min-width: 200px;
}

.slider-container label {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.slider-value {
  font-weight: 700;
  color: var(--primary);
  background: rgba(67, 97, 238, 0.1);
  padding: 0.25rem 0.5rem;
  border-radius: var(--radius-sm);
}

input[type="range"] {
  width: 100%;
  height: 8px;
  border-radius: 4px;
  background: var(--border);
  outline: none;
  -webkit-appearance: none;
  cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: var(--primary);
  cursor: pointer;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
  transition: all 0.2s ease;
}

input[type="range"]::-webkit-slider-thumb:hover {
  background: var(--primary-dark);
  transform: scale(1.1);
}

input[type="range"]::-moz-range-thumb {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: var(--primary);
  cursor: pointer;
  border: none;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

/* ==================== Animation Controls ==================== */
.animation-controls {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
}

.animation-controls .btn {
  min-width: 100px;
}

.animation-controls .step-indicator {
  margin-left: var(--spacing-md);
  padding: 0.5rem 1rem;
  background: rgba(67, 97, 238, 0.1);
  border-radius: var(--radius-sm);
  font-weight: 600;
  color: var(--primary);
}

/* ==================== Graph SVG Styling ==================== */
.graph-svg {
  background: #fafbfc;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  width: 100%;
  height: auto;
}

.graph-edge {
  stroke: #bbb;
  stroke-width: 2;
  fill: none;
  transition: stroke 0.2s, stroke-width 0.2s;
}

.graph-edge.highlighted {
  stroke: var(--primary);
  stroke-width: 3;
}

.graph-edge.path-edge {
  stroke: var(--accent);
  stroke-width: 3.5;
  stroke-dasharray: 8 4;
  animation: dash 1s linear infinite;
}

@keyframes dash {
  to {
    stroke-dashoffset: -12;
  }
}

.graph-node {
  fill: var(--primary);
  stroke: white;
  stroke-width: 2.5;
  cursor: pointer;
  transition: fill 0.2s, r 0.3s, stroke-width 0.2s;
}

.graph-node.selected {
  fill: var(--accent);
  stroke: white;
  stroke-width: 3;
  filter: drop-shadow(0 0 6px rgba(247, 37, 133, 0.4));
}

.graph-node.highlighted {
  fill: var(--success);
}

.graph-node.neighbor {
  fill: var(--secondary);
}

.graph-node.hovered {
  fill: var(--primary-light);
  stroke-width: 3;
}

.graph-label {
  fill: white;
  font-size: 12px;
  font-weight: 600;
  text-anchor: middle;
  dominant-baseline: central;
  pointer-events: none;
  user-select: none;
}

.graph-node-group {
  cursor: move;
}

/* ==================== Section Styling ==================== */
.section {
  margin-bottom: var(--spacing-2xl);
}

.section-title {
  font-size: 2rem;
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-md);
  border-bottom: 3px solid var(--primary);
}

.section-subtitle {
  font-size: 1.5rem;
  color: var(--text-light);
  margin-bottom: var(--spacing-md);
}

/* ==================== Tabs / Pills ==================== */
.tabs {
  display: flex;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-lg);
  flex-wrap: wrap;
}

.tab {
  padding: 0.5rem 1.2rem;
  border: 2px solid var(--primary);
  background: transparent;
  color: var(--primary);
  border-radius: 50px;
  cursor: pointer;
  font-weight: 600;
  transition: all 0.2s ease;
}

.tab:hover {
  background: rgba(67, 97, 238, 0.1);
}

.tab.active {
  background: var(--primary);
  color: white;
}

/* ==================== Badges ==================== */
.badge {
  display: inline-block;
  padding: 0.25rem 0.75rem;
  border-radius: 50px;
  font-size: 0.875rem;
  font-weight: 600;
  line-height: 1;
}

.badge-primary {
  background: var(--primary);
  color: white;
}

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

.badge-warning {
  background: var(--warning);
  color: var(--text);
}

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

.badge-secondary {
  background: var(--secondary);
  color: white;
}

/* ==================== Split Panel Layout ==================== */
.split-panel {
  display: grid;
  grid-template-columns: 60% 40%;
  gap: var(--spacing-lg);
  margin: var(--spacing-lg) 0;
}

.panel-left, .panel-right {
  background: var(--card-bg);
  padding: var(--spacing-lg);
  border-radius: var(--radius);
  box-shadow: 0 2px 8px var(--shadow);
}

@media (max-width: 1024px) {
  .split-panel {
    grid-template-columns: 1fr;
  }
}

/* ==================== Concept List ==================== */
.concept-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.concept-list li {
  background: var(--card-bg);
  padding: var(--spacing-lg);
  border-radius: var(--radius);
  box-shadow: 0 2px 4px var(--shadow);
  border-left: 4px solid var(--primary);
  transition: all 0.2s ease;
}

.concept-list li:hover {
  box-shadow: 0 4px 12px var(--shadow-md);
  transform: translateX(4px);
}

.concept-list .concept-number {
  display: inline-block;
  width: 32px;
  height: 32px;
  background: var(--primary);
  color: white;
  border-radius: 50%;
  text-align: center;
  line-height: 32px;
  font-weight: 700;
  margin-right: var(--spacing-md);
}

/* ==================== Quiz Styling ==================== */
.quiz {
  background: var(--card-bg);
  padding: var(--spacing-xl);
  border-radius: var(--radius);
  box-shadow: 0 2px 8px var(--shadow);
  margin: var(--spacing-lg) 0;
}

.quiz-question {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: var(--spacing-lg);
  color: var(--text);
}

.quiz-options {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.quiz-option {
  padding: var(--spacing-md);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
  background: var(--card-bg);
}

.quiz-option:hover {
  border-color: var(--primary);
  background: rgba(67, 97, 238, 0.05);
}

.quiz-option.correct {
  border-color: var(--success);
  background: rgba(6, 214, 160, 0.1);
  color: var(--success);
  font-weight: 600;
}

.quiz-option.incorrect {
  border-color: var(--danger);
  background: rgba(239, 71, 111, 0.1);
  color: var(--danger);
  font-weight: 600;
}

.quiz-feedback {
  margin-top: var(--spacing-lg);
  padding: var(--spacing-md);
  border-radius: var(--radius-sm);
  background: rgba(67, 97, 238, 0.05);
  border-left: 4px solid var(--primary);
}

.quiz-hint {
  margin-top: var(--spacing-md);
  padding: var(--spacing-md);
  background: rgba(255, 209, 102, 0.15);
  border-left: 4px solid var(--warning);
  border-radius: var(--radius-sm);
}

.quiz-hint summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--text);
  user-select: none;
}

/* ==================== Progress / Step Indicator ==================== */
.step-indicator {
  display: flex;
  gap: var(--spacing-md);
  align-items: center;
  margin: var(--spacing-lg) 0;
  justify-content: center;
}

.step {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--border);
  color: var(--text-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  transition: all 0.3s ease;
  position: relative;
}

.step.active {
  background: var(--primary);
  color: white;
  transform: scale(1.2);
}

.step.completed {
  background: var(--success);
  color: white;
}

.step::after {
  content: '';
  position: absolute;
  left: 100%;
  width: var(--spacing-md);
  height: 2px;
  background: var(--border);
}

.step:last-child::after {
  display: none;
}

.step.completed::after {
  background: var(--success);
}

/* ==================== Learning Path Cards ==================== */
.learning-path-card {
  display: flex;
  gap: var(--spacing-lg);
  background: var(--card-bg);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: 0 2px 8px var(--shadow);
  transition: all 0.3s ease;
  cursor: pointer;
  border-left: 5px solid var(--primary);
}

.learning-path-card:hover {
  box-shadow: 0 8px 24px var(--shadow-lg);
  transform: translateY(-4px);
}

.learning-path-card .path-number {
  flex-shrink: 0;
  width: 60px;
  height: 60px;
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.75rem;
  font-weight: 700;
}

.learning-path-card .path-content {
  flex: 1;
}

.learning-path-card .path-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  color: var(--text);
}

.learning-path-card .path-description {
  color: var(--text-light);
  margin-bottom: var(--spacing-md);
}

.learning-path-card .path-link {
  color: var(--primary);
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.learning-path-card .path-link::after {
  content: '→';
}

/* ==================== Node Info Panel ==================== */
.node-info {
  background: var(--card-bg);
  padding: var(--spacing-lg);
  border-radius: var(--radius);
  box-shadow: 0 2px 8px var(--shadow);
  border-left: 4px solid var(--accent);
}

.node-info h3 {
  color: var(--accent);
  margin-bottom: var(--spacing-md);
}

.node-info .info-row {
  display: flex;
  justify-content: space-between;
  padding: var(--spacing-sm) 0;
  border-bottom: 1px solid var(--border);
}

.node-info .info-label {
  font-weight: 600;
  color: var(--text-light);
}

.node-info .info-value {
  font-weight: 700;
  color: var(--text);
}

/* ==================== Community Colors ==================== */
.community-1 {
  background-color: var(--community-1);
  color: white;
}

.community-2 {
  background-color: var(--community-2);
  color: white;
}

.community-3 {
  background-color: var(--community-3);
  color: white;
}

.community-4 {
  background-color: var(--community-4);
  color: var(--text);
}

.community-5 {
  background-color: var(--community-5);
  color: white;
}

.community-dot-1,
.community-dot-2,
.community-dot-3,
.community-dot-4,
.community-dot-5 {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  margin-right: var(--spacing-sm);
}

.community-dot-1 { background-color: var(--community-1); }
.community-dot-2 { background-color: var(--community-2); }
.community-dot-3 { background-color: var(--community-3); }
.community-dot-4 { background-color: var(--community-4); }
.community-dot-5 { background-color: var(--community-5); }

/* ==================== Accessibility ==================== */
*:focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 2px;
}

/* Respect user preference for reduced motion */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* Ensure sufficient color contrast */
.text-contrast {
  color: var(--text);
}

/* ==================== Scrollbar Styling ==================== */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg);
}

::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-lighter);
}

/* ==================== Print Styles ==================== */
@media print {
  .nav,
  .controls,
  .animation-controls,
  .btn {
    display: none !important;
  }

  .card,
  .info-panel,
  .quiz {
    box-shadow: none;
    page-break-inside: avoid;
  }

  body {
    background: white;
  }
}

/* ==================== Utility Classes ==================== */
.text-center {
  text-align: center;
}

.text-left {
  text-align: left;
}

.text-right {
  text-align: right;
}

.mt-sm { margin-top: var(--spacing-sm); }
.mt-md { margin-top: var(--spacing-md); }
.mt-lg { margin-top: var(--spacing-lg); }
.mt-xl { margin-top: var(--spacing-xl); }

.mb-sm { margin-bottom: var(--spacing-sm); }
.mb-md { margin-bottom: var(--spacing-md); }
.mb-lg { margin-bottom: var(--spacing-lg); }
.mb-xl { margin-bottom: var(--spacing-xl); }

.p-sm { padding: var(--spacing-sm); }
.p-md { padding: var(--spacing-md); }
.p-lg { padding: var(--spacing-lg); }
.p-xl { padding: var(--spacing-xl); }

.hidden {
  display: none;
}

.visible {
  display: block;
}

/* ==================== Responsive Images ==================== */
img {
  max-width: 100%;
  height: auto;
}

/* ==================== Loading States ==================== */
.loading {
  opacity: 0.6;
  pointer-events: none;
}

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

.spinner {
  width: 40px;
  height: 40px;
  border: 4px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin: var(--spacing-xl) auto;
}

/* ==================== Hero Section (index.html) ==================== */
.hero {
  text-align: center;
  padding: var(--spacing-2xl) 0;
  margin-bottom: var(--spacing-xl);
}

.hero h1 {
  font-size: 2.75rem;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: var(--spacing-md);
}

.tagline {
  font-size: 1.25rem;
  color: var(--text-light);
  max-width: 600px;
  margin: 0 auto;
}

/* ==================== Learning Path Grid ==================== */
.learning-path-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-lg);
}

@media (max-width: 768px) {
  .learning-path-grid {
    grid-template-columns: 1fr;
  }
}

.learning-path-card .card-number {
  flex-shrink: 0;
  width: 48px;
  height: 48px;
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-md);
}

.learning-path-card .card-description {
  color: var(--text-light);
  margin-bottom: var(--spacing-lg);
  line-height: 1.6;
}

/* ==================== Step Indicator (index.html) ==================== */
.step-indicator {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  margin: var(--spacing-lg) 0;
}

.step-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--spacing-xs);
}

.step-number {
  width: 36px;
  height: 36px;
  background: var(--primary);
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.9rem;
}

.step-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-light);
}

.step-arrow {
  font-size: 1.25rem;
  color: var(--text-lighter);
  margin: 0 var(--spacing-xs);
}

/* ==================== Footer CTA ==================== */
.footer-cta {
  text-align: center;
  margin-top: var(--spacing-2xl);
}

.cta-box {
  background: linear-gradient(135deg, #f0f4ff, #fce4f0);
  padding: var(--spacing-2xl);
  border-radius: var(--radius-lg);
}

.cta-box h3 {
  margin-bottom: var(--spacing-sm);
}

.cta-box p {
  color: var(--text-light);
  margin-bottom: var(--spacing-lg);
}

/* ==================== Graph Basics Page ==================== */
.intro-text {
  font-size: 1.15rem;
  color: var(--text-light);
  margin-bottom: var(--spacing-xl);
}

.graph-container {
  margin: var(--spacing-lg) 0;
  min-height: 300px;
}

.concept-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-lg);
}

@media (max-width: 1024px) {
  .concept-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .concept-grid {
    grid-template-columns: 1fr;
  }
}

.concept-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 8px var(--shadow);
  border-top: 3px solid var(--primary);
  transition: all 0.2s ease;
}

.concept-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 16px var(--shadow-md);
}

.concept-card h3 {
  font-size: 1.1rem;
  color: var(--primary-dark);
  margin-bottom: var(--spacing-sm);
}

.caption {
  font-size: 0.9rem;
  color: var(--text-light);
  font-style: italic;
  text-align: center;
  margin-top: var(--spacing-sm);
}

.note {
  font-size: 0.95rem;
  color: var(--text-light);
  margin-top: var(--spacing-md);
}

.btn-small, .btn.btn-small {
  padding: 0.4rem 1rem;
  font-size: 0.9rem;
  border-radius: var(--radius-sm);
  border: 2px solid var(--primary);
  background: transparent;
  color: var(--primary);
  cursor: pointer;
  font-weight: 600;
  transition: all 0.2s ease;
}

.btn-small:hover, .btn.btn-small:hover {
  background: rgba(67, 97, 238, 0.1);
}

.btn-small.active, .btn.btn-small.active {
  background: var(--primary);
  color: white;
}

.button-group {
  display: flex;
  gap: var(--spacing-sm);
}

.nav-footer {
  display: flex;
  justify-content: space-between;
  margin-top: var(--spacing-2xl);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--border);
}

/* Adjacency matrix table */
.matrix-container {
  overflow-x: auto;
  margin: var(--spacing-md) 0;
}

.adjacency-matrix {
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: 0.9rem;
}

.adjacency-matrix th,
.adjacency-matrix td {
  width: 40px;
  height: 40px;
  text-align: center;
  border: 1px solid var(--border);
  padding: 0.25rem;
}

.adjacency-matrix th {
  background: var(--primary);
  color: white;
  font-weight: 700;
}

.adjacency-matrix td {
  background: var(--card-bg);
}

.adjacency-list {
  padding: var(--spacing-md);
  font-family: var(--font-mono);
  font-size: 0.95rem;
  line-height: 1.8;
}

.color-badge {
  display: inline-block;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  margin-right: var(--spacing-sm);
  vertical-align: middle;
}

.error {
  color: var(--danger);
  font-weight: 600;
}