/* =========================================================================
   Graph ML Lab -- Academic Demo Stylesheet
   Light theme, serif headings, clean academic layout
   ========================================================================= */

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

:root {
  --color-bg:        #fafaf9;
  --color-surface:   #ffffff;
  --color-text:      #1a1a2e;
  --color-text-mute: #5a5a72;
  --color-accent:    #3730a3;
  --color-accent-lt: #6366f1;
  --color-accent-bg: #eef2ff;
  --color-border:    #e2e2ea;
  --color-code-bg:   #f5f5f7;
  --color-success:   #059669;
  --color-warn:      #d97706;
  --color-community0:#6366f1;
  --color-community1:#f59e0b;
  --font-heading:    'Playfair Display', 'Georgia', serif;
  --font-body:       'Source Sans 3', 'Segoe UI', system-ui, sans-serif;
  --font-mono:       'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
  --max-w:           1120px;
  --section-py:      6rem;
  --radius:          8px;
  --shadow-sm:       0 1px 3px rgba(0,0,0,0.06);
  --shadow-md:       0 4px 16px rgba(0,0,0,0.08);
  --shadow-lg:       0 8px 32px rgba(0,0,0,0.10);
  --transition:      0.3s cubic-bezier(0.4,0,0.2,1);
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

/* --- Typography --- */
h1, h2, h3, h4 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.25;
  color: var(--color-text);
}

h1 { font-size: 3rem; letter-spacing: -0.02em; }
h2 { font-size: 2.25rem; letter-spacing: -0.01em; margin-bottom: 0.5em; }
h3 { font-size: 1.5rem; margin-bottom: 0.4em; }
h4 { font-size: 1.125rem; }

p {
  max-width: 65ch;
  margin-bottom: 1em;
  color: var(--color-text-mute);
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition);
}
a:hover {
  color: var(--color-accent-lt);
  text-decoration: underline;
}

/* --- Layout --- */
.container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 2rem;
}

section {
  padding: var(--section-py) 0;
  position: relative;
}

section + section {
  border-top: 1px solid var(--color-border);
}

.section-label {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-accent);
  background: var(--color-accent-bg);
  padding: 0.25em 0.75em;
  border-radius: 999px;
  margin-bottom: 1rem;
}

.section-desc {
  font-size: 1.1rem;
  max-width: 60ch;
  margin-bottom: 2.5rem;
}

/* --- Navigation --- */
nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: rgba(250,250,249,0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  transition: box-shadow var(--transition);
}

nav.scrolled {
  box-shadow: var(--shadow-sm);
}

nav .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 3.5rem;
}

.nav-brand {
  font-family: var(--font-heading);
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--color-text);
  text-decoration: none;
}

.nav-links {
  display: flex;
  gap: 1.75rem;
  list-style: none;
}

.nav-links a {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text-mute);
  text-decoration: none;
  transition: color var(--transition);
  position: relative;
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--color-accent);
  transition: width var(--transition);
}

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

.nav-links a:hover::after,
.nav-links a.active::after {
  width: 100%;
}

/* --- Hero --- */
.hero {
  padding: 10rem 0 6rem;
  text-align: center;
  background: linear-gradient(180deg, var(--color-accent-bg) 0%, var(--color-bg) 100%);
  border-bottom: none;
}

.hero h1 {
  margin-bottom: 0.4em;
  background: linear-gradient(135deg, var(--color-accent) 0%, var(--color-accent-lt) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero .tagline {
  font-size: 1.2rem;
  color: var(--color-text-mute);
  max-width: 58ch;
  margin: 0 auto 2rem;
  line-height: 1.6;
}

.hero-links {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.hero-stack {
  display: flex;
  justify-content: center;
  gap: 0.6rem;
  margin-top: 1.5rem;
  flex-wrap: wrap;
}

.stack-tag {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--color-accent);
  background: var(--color-accent-bg);
  border: 1px solid rgba(99,102,241,0.15);
  padding: 0.2em 0.65em;
  border-radius: 4px;
  letter-spacing: 0.02em;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5em;
  padding: 0.65em 1.5em;
  border-radius: var(--radius);
  font-size: 0.9rem;
  font-weight: 600;
  font-family: var(--font-body);
  text-decoration: none;
  transition: all var(--transition);
  cursor: pointer;
  border: none;
}

.btn-primary {
  background: var(--color-accent);
  color: #fff;
}
.btn-primary:hover {
  background: var(--color-accent-lt);
  color: #fff;
  text-decoration: none;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-outline {
  background: transparent;
  color: var(--color-accent);
  border: 1.5px solid var(--color-accent);
}
.btn-outline:hover {
  background: var(--color-accent-bg);
  text-decoration: none;
  transform: translateY(-1px);
}

/* --- Cards --- */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.5rem;
  transition: box-shadow var(--transition), transform var(--transition);
}
.card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

/* --- Graph Visualization Containers --- */
.graph-container {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  position: relative;
}

.graph-container svg {
  display: block;
  width: 100%;
  height: 100%;
}

/* D3 graph styles */
.graph-container .node circle {
  stroke: #fff;
  stroke-width: 2px;
  cursor: pointer;
  transition: r 0.2s ease;
}
.graph-container .node circle:hover {
  filter: brightness(1.15);
}

.graph-container .node text {
  font-family: var(--font-mono);
  font-size: 10px;
  fill: #fff;
  pointer-events: none;
  text-anchor: middle;
  dominant-baseline: central;
  font-weight: 600;
}

.graph-container .link {
  stroke: #c7c7d4;
  stroke-width: 1.5;
  stroke-opacity: 0.6;
  transition: stroke var(--transition), stroke-opacity var(--transition);
}

.graph-container .link.highlighted {
  stroke: var(--color-accent-lt);
  stroke-width: 3;
  stroke-opacity: 1;
}

.graph-container .link.message-active {
  stroke: var(--color-accent);
  stroke-width: 3.5;
  stroke-opacity: 1;
  filter: drop-shadow(0 0 4px rgba(99,102,241,0.4));
}

.graph-container .node.pulse circle {
  animation: nodePulse 0.6s ease-out;
}

@keyframes nodePulse {
  0%   { transform: scale(1); filter: brightness(1); }
  50%  { transform: scale(1.4); filter: brightness(1.3); }
  100% { transform: scale(1); filter: brightness(1); }
}

/* --- GNN Section --- */
.gnn-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  align-items: start;
}

.gnn-graph-panel {
  min-height: 440px;
}

.gnn-info-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.message-controls {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 1rem;
}

.legend {
  display: flex;
  gap: 1.5rem;
  font-size: 0.85rem;
  color: var(--color-text-mute);
  align-items: center;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 0.4em;
}

.legend-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  display: inline-block;
}

/* --- Metrics Display --- */
.metrics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 1rem;
}

.metric-card {
  text-align: center;
  padding: 1.25rem 1rem;
}

.metric-value {
  font-family: var(--font-heading);
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--color-accent);
  display: block;
  line-height: 1.2;
}

.metric-label {
  font-size: 0.8rem;
  color: var(--color-text-mute);
  margin-top: 0.25em;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* --- Generator Section --- */
.generator-controls {
  display: flex;
  gap: 1.5rem;
  align-items: flex-end;
  flex-wrap: wrap;
  margin-bottom: 2rem;
  padding: 1.5rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.control-group label {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-text-mute);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.control-group input[type="range"] {
  width: 160px;
  accent-color: var(--color-accent);
}

.control-group .range-value {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-accent);
  font-weight: 600;
  min-width: 3ch;
  text-align: right;
}

.control-group select {
  padding: 0.45em 0.75em;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-family: var(--font-body);
  font-size: 0.9rem;
  background: var(--color-surface);
  color: var(--color-text);
  cursor: pointer;
}

.graph-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
}

.graph-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: box-shadow var(--transition), transform var(--transition);
}
.graph-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.graph-card-viz {
  height: 200px;
  background: var(--color-code-bg);
  position: relative;
}

.graph-card-info {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--color-border);
}

.graph-card-info h4 {
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.95rem;
  margin-bottom: 0.5rem;
}

.graph-props {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.25rem 1rem;
  font-size: 0.8rem;
  color: var(--color-text-mute);
}

.graph-props span {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--color-text);
}

/* --- VAE Section --- */
.vae-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 3rem;
}

.interpolation-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 2rem;
}

.interpolation-slider-wrap {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.interpolation-slider-wrap label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-mute);
  white-space: nowrap;
}

.interpolation-slider-wrap input[type="range"] {
  flex: 1;
  accent-color: var(--color-accent);
  height: 6px;
}

.interpolation-slider-wrap .alpha-value {
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--color-accent);
  min-width: 4ch;
}

.interpolation-graph {
  height: 320px;
  background: var(--color-code-bg);
  border-radius: var(--radius);
  overflow: hidden;
  margin-bottom: 1rem;
}

.interpolation-endpoints {
  display: flex;
  justify-content: space-between;
  font-size: 0.85rem;
  color: var(--color-text-mute);
}

.interpolation-endpoints .endpoint-label {
  display: flex;
  align-items: center;
  gap: 0.4em;
}

.endpoint-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
}

/* Architecture diagram */
.architecture-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 2rem;
}

.arch-diagram {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  padding: 2rem 1rem;
  overflow-x: auto;
}

.arch-block {
  text-align: center;
  padding: 1rem 1.25rem;
  border-radius: var(--radius);
  min-width: 120px;
  position: relative;
}

.arch-block.input-block  { background: #dbeafe; border: 1.5px solid #93c5fd; }
.arch-block.encoder-block { background: #e0e7ff; border: 1.5px solid #a5b4fc; }
.arch-block.latent-block  { background: #ede9fe; border: 1.5px solid #c4b5fd; }
.arch-block.decoder-block { background: #fce7f3; border: 1.5px solid #f9a8d4; }
.arch-block.output-block  { background: #d1fae5; border: 1.5px solid #6ee7b7; }

.arch-block-title {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 0.25em;
}

.arch-block-desc {
  font-size: 0.8rem;
  color: var(--color-text-mute);
  line-height: 1.3;
}

.arch-arrow {
  font-size: 1.5rem;
  color: var(--color-text-mute);
  padding: 0 0.5rem;
  flex-shrink: 0;
}

/* --- Training Curve Chart --- */
.chart-container {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-top: 2rem;
}

.chart-container h4 {
  margin-bottom: 1rem;
}

.chart-area {
  height: 220px;
  position: relative;
}

/* --- Code blocks --- */
.code-block {
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.65;
  overflow-x: auto;
  color: var(--color-text);
}

.code-block .keyword  { color: #7c3aed; }
.code-block .string   { color: #059669; }
.code-block .comment  { color: #9ca3af; font-style: italic; }
.code-block .number   { color: #d97706; }

/* --- Footer --- */
footer {
  padding: 3rem 0;
  border-top: 1px solid var(--color-border);
  background: var(--color-surface);
}

.footer-content {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2rem;
}

.footer-col h4 {
  font-family: var(--font-body);
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-text-mute);
  margin-bottom: 0.75rem;
}

.footer-col ul {
  list-style: none;
}

.footer-col li {
  margin-bottom: 0.4rem;
}

.footer-col a {
  font-size: 0.9rem;
  color: var(--color-text-mute);
}
.footer-col a:hover {
  color: var(--color-accent);
}

.footer-citation {
  margin-top: 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--color-border);
}

.footer-citation .code-block {
  font-size: 0.75rem;
  max-width: 700px;
}

.footer-bottom {
  margin-top: 2rem;
  text-align: center;
  font-size: 0.8rem;
  color: var(--color-text-mute);
}

/* --- Scroll Animations --- */
.fade-in {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

.fade-in-delay-1 { transition-delay: 0.1s; }
.fade-in-delay-2 { transition-delay: 0.2s; }
.fade-in-delay-3 { transition-delay: 0.3s; }

/* --- Status Badge --- */
.status-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35em;
  padding: 0.2em 0.65em;
  border-radius: 999px;
  font-size: 0.75rem;
  font-weight: 600;
  font-family: var(--font-mono);
}

.status-badge.running {
  background: #dcfce7;
  color: #166534;
}

.status-badge.running::before {
  content: '';
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: #22c55e;
  animation: blink 1.5s infinite;
}

@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.3; }
}

/* --- Tooltip --- */
.tooltip {
  position: absolute;
  background: var(--color-text);
  color: #fff;
  padding: 0.4em 0.7em;
  border-radius: 4px;
  font-size: 0.78rem;
  font-family: var(--font-mono);
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.15s;
  z-index: 50;
  white-space: nowrap;
}

.tooltip.show {
  opacity: 1;
}

/* --- Responsive --- */
@media (max-width: 900px) {
  :root {
    --section-py: 4rem;
  }

  h1 { font-size: 2.25rem; }
  h2 { font-size: 1.75rem; }

  .gnn-layout {
    grid-template-columns: 1fr;
  }

  .graph-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .arch-diagram {
    flex-wrap: wrap;
    gap: 0.5rem;
  }

  .arch-arrow {
    display: none;
  }
}

@media (max-width: 600px) {
  .container {
    padding: 0 1rem;
  }

  h1 { font-size: 1.75rem; }
  h2 { font-size: 1.5rem; }

  .hero {
    padding: 7rem 0 4rem;
  }

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

  .nav-links {
    gap: 1rem;
  }

  .nav-links a {
    font-size: 0.8rem;
  }

  .generator-controls {
    flex-direction: column;
    align-items: stretch;
  }

  .control-group input[type="range"] {
    width: 100%;
  }

  .footer-content {
    grid-template-columns: 1fr;
  }

  .metrics-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* --- Spatial 3D Section --- */
.spatial-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  align-items: start;
}

.spatial-info-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.spatial-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.25rem;
}

.spatial-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: box-shadow var(--transition), transform var(--transition);
}
.spatial-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.spatial-card-viz {
  height: 200px;
  background: var(--color-code-bg);
  position: relative;
}

.spatial-card-info {
  padding: 0.75rem 1rem;
  border-top: 1px solid var(--color-border);
}

.spatial-card-info h4 {
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.85rem;
  margin-bottom: 0.25rem;
}

.spatial-card-info .spatial-props {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  font-size: 0.75rem;
  color: var(--color-text-mute);
}

.spatial-card-info .spatial-props span {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--color-text);
}

/* Spatial tree SVG: indigo nodes + edges */
.spatial-card-viz .tree-edge {
  stroke: #818cf8;
  stroke-width: 1.5;
  stroke-opacity: 0.55;
}

.spatial-card-viz .tree-node {
  fill: #4f46e5;
  stroke: #fff;
  stroke-width: 1;
}

/* --- Mesh Section --- */
.mesh-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 3rem;
}

.mesh-subtitle {
  font-size: 0.95rem;
  margin-bottom: 1.5rem;
}

.mesh-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
}

.mesh-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: box-shadow var(--transition), transform var(--transition);
}
.mesh-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.mesh-card-viz {
  height: 180px;
  background: var(--color-code-bg);
  position: relative;
}

.mesh-card-info {
  padding: 0.75rem 1rem;
  border-top: 1px solid var(--color-border);
}

.mesh-card-info h4 {
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.85rem;
  margin-bottom: 0.25rem;
}

.mesh-card-info .mesh-props {
  display: flex;
  gap: 0.75rem;
  font-size: 0.75rem;
  color: var(--color-text-mute);
}

.mesh-card-info .mesh-props span {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--color-text);
}

/* Mesh SVG: pink wireframe */
.mesh-card-viz .mesh-edge,
.mesh-interp-step-viz .mesh-edge {
  stroke: #ec4899;
  stroke-width: 1;
  stroke-opacity: 0.5;
}

.mesh-card-viz .mesh-node,
.mesh-interp-step-viz .mesh-node {
  fill: #ec4899;
  stroke: #fff;
  stroke-width: 0.8;
}

/* --- Method Panel --- */
.method-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 2rem;
}

.method-steps {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  margin-top: 1rem;
}

.method-step {
  display: flex;
  gap: 1rem;
  align-items: flex-start;
}

.method-step-num {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--color-accent-bg);
  color: var(--color-accent);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  flex-shrink: 0;
  border: 1.5px solid rgba(99,102,241,0.2);
}

.method-step strong {
  font-size: 0.95rem;
  color: var(--color-text);
  display: block;
  margin-bottom: 0.2em;
}

.method-step p {
  font-size: 0.88rem;
  color: var(--color-text-mute);
  line-height: 1.5;
  margin-bottom: 0;
}

.method-step code {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  background: var(--color-code-bg);
  padding: 0.1em 0.35em;
  border-radius: 3px;
  color: var(--color-accent);
}

/* --- Interpolation Strips (multiple) --- */
.interp-subtitle {
  font-size: 0.92rem;
  color: var(--color-text-mute);
  margin-bottom: 1.5rem;
}

.interp-pair {
  margin-bottom: 2rem;
}

.interp-pair:last-child {
  margin-bottom: 0;
}

.interp-pair-title {
  font-family: var(--font-body);
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.6em;
}

.interp-pair-title .pair-arrow {
  color: var(--color-text-mute);
  font-size: 1.1em;
}

.interp-pair-meta {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-mute);
  margin-bottom: 0.5rem;
}

.mesh-interp-strip {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
  gap: 0.75rem;
  padding: 0.5rem 0;
}

.mesh-interp-step {
  text-align: center;
  min-width: 0;
}

.mesh-interp-step-viz {
  width: 100%;
  aspect-ratio: 1;
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  position: relative;
}

.mesh-interp-step-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-mute);
  margin-top: 0.4rem;
  font-weight: 600;
}

.mesh-interp-step.is-endpoint .mesh-interp-step-viz {
  border-color: #ec4899;
  border-width: 1.5px;
}

.mesh-interp-step.is-endpoint .mesh-interp-step-label {
  color: #ec4899;
  font-weight: 700;
}

/* --- Graph Geometric Interpolation Strips --- */
.graph-interp-pair {
  margin-bottom: 1.5rem;
}

.graph-interp-pair h4 {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-text-mute);
  margin-bottom: 0.5rem;
  font-weight: 500;
}

.graph-interp-strip {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(90px, 1fr));
  gap: 0.35rem;
  padding: 0.5rem 0;
}

.graph-interp-step {
  text-align: center;
  min-width: 0;
}

.graph-interp-step-viz {
  width: 100%;
  aspect-ratio: 1;
  background: var(--color-code-bg);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  overflow: hidden;
  position: relative;
}

.graph-interp-step-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-mute);
  margin-top: 0.15rem;
  font-weight: 600;
}

.graph-interp-step.is-endpoint .graph-interp-step-viz {
  border-color: var(--color-accent-lt);
  border-width: 1.5px;
}

.graph-interp-step.is-endpoint .graph-interp-step-label {
  color: var(--color-accent);
  font-weight: 700;
}

/* Architecture description */
.arch-desc {
  font-size: 0.9rem;
  color: var(--color-text-mute);
  margin-bottom: 0.5rem;
  max-width: 65ch;
}

/* --- Responsive: spatial & mesh --- */
@media (max-width: 900px) {
  .spatial-layout {
    grid-template-columns: 1fr;
  }
  .mesh-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 600px) {
  .spatial-grid {
    grid-template-columns: 1fr;
  }
  .mesh-grid {
    grid-template-columns: 1fr;
  }
  .mesh-interp-strip {
    grid-template-columns: repeat(4, 1fr);
  }
  .method-step {
    flex-direction: column;
    gap: 0.5rem;
  }
}

/* --- Physics GNN Section --- */
.physics-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  align-items: start;
}

.physics-viz-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.physics-demo-graphs {
  display: flex;
  gap: 1.25rem;
}

.physics-graph-panel {
  flex: 1;
  min-width: 0;
}

.physics-graph-panel h4 {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-mute);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 0.5rem;
  text-align: center;
}

.physics-graph-viz {
  width: 100%;
  aspect-ratio: 1;
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
}

.physics-graph-viz svg {
  width: 100%;
  height: 100%;
}

.physics-edge {
  stroke: var(--color-text-mute);
  stroke-width: 1.5;
  stroke-opacity: 0.35;
}

.physics-node {
  transition: fill 0.3s ease;
}

@media (max-width: 900px) {
  .physics-layout {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 600px) {
  .physics-demo-graphs {
    flex-direction: column;
  }
}

/* --- Hyperbolic GNN Section --- */
.hyperbolic-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 3rem;
  align-items: start;
}

.hyperbolic-viz-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.hyperbolic-demo-disk {
  display: flex;
  justify-content: center;
  align-items: center;
}

.hyperbolic-demo-disk svg {
  width: 100%;
  max-width: 300px;
  height: auto;
}

.hyperbolic-boundary {
  fill: none;
  stroke: var(--color-text-mute);
  stroke-width: 0.02;
  stroke-dasharray: 0.04 0.02;
  opacity: 0.6;
}

.hyperbolic-grid-circle {
  fill: none;
  stroke: var(--color-border);
  stroke-width: 0.008;
  stroke-dasharray: 0.02 0.015;
  opacity: 0.5;
}

.hyperbolic-edge {
  fill: none;
  stroke: var(--color-text-mute);
  stroke-width: 0.02;
  stroke-opacity: 0.5;
  stroke-linecap: round;
}

.hyperbolic-node {
  stroke: #fff;
  stroke-width: 0.02;
  transition: fill 0.3s ease;
}

@media (max-width: 900px) {
  .hyperbolic-layout {
    grid-template-columns: 1fr;
  }
}

/* --- WL Test Section --- */
.wl-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 3rem;
}

.wl-pairs-panel {
  display: flex;
  flex-direction: column;
  gap: 2.5rem;
}

.wl-pair {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 2rem;
  transition: box-shadow var(--transition);
}

.wl-pair:hover {
  box-shadow: var(--shadow-md);
}

.wl-pair-header {
  margin-bottom: 1.5rem;
}

.wl-pair-title-row {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 0.5rem;
  flex-wrap: wrap;
}

.wl-pair-title {
  font-family: var(--font-body);
  font-size: 1.15rem;
  font-weight: 700;
  margin-bottom: 0;
}

.wl-pair-desc {
  font-size: 0.88rem;
  color: var(--color-text-mute);
  line-height: 1.5;
  margin-bottom: 0;
  max-width: 60ch;
}

.wl-verdict-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35em;
  padding: 0.3em 0.85em;
  border-radius: 999px;
  font-size: 0.78rem;
  font-weight: 700;
  font-family: var(--font-mono);
  white-space: nowrap;
}

.wl-verdict-badge.wl-verdict--success {
  background: #dcfce7;
  color: #166534;
  border: 1px solid #86efac;
}

.wl-verdict-badge.wl-verdict--fail {
  background: #fef2f2;
  color: #991b1b;
  border: 1px solid #fca5a5;
}

/* Interactive viewer */
.wl-viewer {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.wl-step-indicator {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
}

.wl-nav-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1.5px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text);
  font-size: 0.9rem;
  cursor: pointer;
  transition: all var(--transition);
}

.wl-nav-btn:hover:not(:disabled) {
  background: var(--color-accent-bg);
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.wl-nav-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.wl-play-btn {
  font-size: 0.75rem;
}

.wl-play-btn.playing {
  background: var(--color-accent-bg);
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.wl-step-text {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--color-accent);
  min-width: 100px;
  text-align: center;
}

.wl-slider-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
}

.wl-slider {
  width: 280px;
  max-width: 100%;
  accent-color: var(--color-accent);
  height: 4px;
  cursor: pointer;
}

.wl-step-dots {
  display: flex;
  gap: 0.5rem;
  justify-content: center;
}

.wl-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--color-border);
  cursor: pointer;
  transition: all var(--transition);
}

.wl-dot.past {
  background: rgba(99, 102, 241, 0.3);
}

.wl-dot.active {
  background: var(--color-accent);
  transform: scale(1.3);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}

/* Graph panels side by side */
.wl-graphs-row {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 1rem;
  align-items: center;
}

.wl-graph-panel {
  text-align: center;
}

.wl-graph-label {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: 0.5rem;
  font-family: var(--font-mono);
}

.wl-graph-viz {
  width: 100%;
  aspect-ratio: 1;
  max-width: 220px;
  margin: 0 auto;
  background: var(--color-code-bg);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  overflow: hidden;
}

.wl-vs {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--color-text-mute);
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

/* Histogram comparison */
.wl-histogram-area {
  padding: 0.75rem 1rem;
  background: var(--color-code-bg);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
}

.wl-histogram-compare {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.wl-hist-row {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.wl-hist-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--color-text-mute);
  min-width: 22px;
  text-align: right;
}

.wl-hist-bar {
  flex: 1;
  display: flex;
  height: 16px;
  border-radius: 3px;
  overflow: hidden;
  background: var(--color-border);
}

.wl-hist-seg {
  height: 100%;
  transition: width 0.4s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
}

.wl-hist-seg:hover {
  filter: brightness(1.15);
}

/* Step match badge */
.wl-step-match {
  text-align: center;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  padding: 0.45em 1.2em;
  border-radius: 999px;
  display: inline-block;
  margin: 0 auto;
  display: block;
  width: fit-content;
  margin: 0 auto;
  transition: all var(--transition);
}

.wl-step-match--same {
  background: #fef2f2;
  color: #991b1b;
  border: 1px solid #fca5a5;
}

.wl-step-match--diff {
  background: #dcfce7;
  color: #166534;
  border: 1px solid #86efac;
}

/* Color count info */
.wl-color-info {
  display: flex;
  justify-content: center;
  gap: 2rem;
  font-size: 0.8rem;
  color: var(--color-text-mute);
  font-family: var(--font-mono);
}

.wl-color-info strong {
  color: var(--color-accent);
}

@media (max-width: 600px) {
  .wl-graphs-row {
    grid-template-columns: 1fr;
    gap: 0.5rem;
  }
  .wl-vs {
    display: none;
  }
  .wl-graph-viz {
    max-width: 180px;
  }
  .wl-slider {
    width: 200px;
  }
}

/* --- Utility --- */
.text-center { text-align: center; }
.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mt-4 { margin-top: 2rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }

/* ── Guide Section ────────────────────────────────────────── */
.guide-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.5rem;
}

.guide-card-demo {
  padding: 1.5rem;
}

.guide-card-demo h3 {
  font-family: var(--font-heading);
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: 0.5rem;
}

.guide-card-demo > p {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin-bottom: 1rem;
  line-height: 1.6;
}

.guide-card-demo h4 {
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-accent);
  margin: 1rem 0 0.5rem;
  padding-bottom: 0.25rem;
  border-bottom: 1px solid var(--color-border);
}

.guide-card-demo ol {
  padding-left: 1.5rem;
  margin: 0;
}

.guide-card-demo ol li {
  font-size: 0.88rem;
  color: var(--color-text-muted);
  line-height: 1.65;
  margin-bottom: 0.35rem;
}

.guide-card-demo ol li em {
  color: var(--color-text);
}

.guide-card-demo ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.guide-card-demo ul li {
  position: relative;
  padding-left: 1rem;
  font-size: 0.88rem;
  color: var(--color-text-muted);
  line-height: 1.65;
  margin-bottom: 0.35rem;
}

.guide-card-demo ul li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.55em;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--color-accent);
}

@media (max-width: 800px) {
  .guide-grid {
    grid-template-columns: 1fr;
  }
}

/* =========================================================================
   Dark Mode
   ========================================================================= */

.theme-toggle {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 200;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  box-shadow: var(--shadow-md);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  transition: background var(--transition), border-color var(--transition);
}
.theme-toggle:hover {
  box-shadow: var(--shadow-lg);
}
.theme-toggle .icon-light,
.theme-toggle .icon-dark {
  position: absolute;
  transition: opacity 0.2s ease;
}
[data-theme="dark"] .theme-toggle .icon-light { opacity: 0; }
[data-theme="dark"] .theme-toggle .icon-dark  { opacity: 1; }
[data-theme="light"] .theme-toggle .icon-light { opacity: 1; }
[data-theme="light"] .theme-toggle .icon-dark  { opacity: 0; }

[data-theme="dark"] {
  --color-bg:        #0f1219;
  --color-surface:   #171c28;
  --color-text:      #e2e8f0;
  --color-text-mute: #94a3b8;
  --color-accent:    #818cf8;
  --color-accent-lt: #a5b4fc;
  --color-accent-bg: rgba(99,102,241,0.12);
  --color-border:    #2d3548;
  --color-code-bg:   #1e2433;
  --color-success:   #34d399;
  --color-warn:      #fbbf24;
  --shadow-sm:       0 1px 3px rgba(0,0,0,0.25);
  --shadow-md:       0 4px 16px rgba(0,0,0,0.35);
  --shadow-lg:       0 8px 32px rgba(0,0,0,0.45);
}

[data-theme="dark"] nav {
  background: rgba(15,18,25,0.88);
}

[data-theme="dark"] .hero {
  background: linear-gradient(135deg, #171c28 0%, #1e2433 100%);
}

[data-theme="dark"] .stat-card {
  background: var(--color-surface);
  border-color: var(--color-border);
}

[data-theme="dark"] .method-card {
  background: var(--color-surface);
  border-color: var(--color-border);
}

[data-theme="dark"] .wl-pair {
  background: var(--color-surface);
  border-color: var(--color-border);
}

[data-theme="dark"] .physics-graph-viz {
  background: var(--color-code-bg);
  border-color: var(--color-border);
}

[data-theme="dark"] .physics-edge {
  stroke: #64748b;
  stroke-opacity: 0.7;
}

[data-theme="dark"] .physics-node {
  stroke: var(--color-surface);
}

[data-theme="dark"] .hyperbolic-boundary {
  stroke: #475569;
}

[data-theme="dark"] .hyperbolic-grid-circle {
  stroke: #334155;
}

[data-theme="dark"] .hyperbolic-edge {
  stroke: #64748b;
}

[data-theme="dark"] .hyperbolic-node {
  stroke: var(--color-surface);
}

[data-theme="dark"] .guide-card-demo {
  background: var(--color-surface);
  border-color: var(--color-border);
}

[data-theme="dark"] .theme-toggle {
  background: var(--color-surface);
  border-color: var(--color-border);
}

[data-theme="dark"] .btn--outline {
  border-color: var(--color-border);
  color: var(--color-text);
}

[data-theme="dark"] .btn--outline:hover {
  background: var(--color-accent-bg);
}

[data-theme="dark"] .tag {
  background: var(--color-code-bg);
  color: var(--color-text-mute);
  border-color: var(--color-border);
}