/* === Two Ways of Measuring — Stylesheet === */

:root {
  --bg: #0a0e17;
  --bg-card: #111827;
  --bg-card-hover: #1a2332;
  --text: #d1d5db;
  --text-muted: #9ca3af;
  --text-heading: #f3f4f6;
  --accent: #e2b04a;
  --accent-glow: #f0c96d;
  --accent-dim: #8b6914;
  --border: #1e293b;
  --border-light: #334155;
  --red: #f87171;
  --green: #4ade80;
  --blue: #60a5fa;
  --purple: #a78bfa;
  --cyan: #22d3ee;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 4px 24px rgba(0,0,0,0.3);
  --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-serif: 'Georgia', 'Times New Roman', serif;
  --max-width: 900px;
}

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

html { scroll-behavior: smooth; font-size: 17px; }

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  min-height: 100vh;
}

/* === Background animation === */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background:
    radial-gradient(ellipse 80% 60% at 50% 0%, rgba(226,176,74,0.04) 0%, transparent 60%),
    radial-gradient(ellipse 40% 50% at 80% 80%, rgba(96,165,250,0.03) 0%, transparent 60%);
  pointer-events: none;
  z-index: 0;
}

/* === Navigation === */
nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(10,14,23,0.85);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  padding: 0 1.5rem;
}

.nav-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 56px;
  gap: 1rem;
}

.nav-logo {
  font-family: var(--font-serif);
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--accent);
  text-decoration: none;
  letter-spacing: -0.02em;
  white-space: nowrap;
}

.nav-logo:hover { color: var(--accent-glow); }

.nav-links {
  display: flex;
  gap: 0.25rem;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.nav-links a {
  color: var(--text-muted);
  text-decoration: none;
  padding: 0.35rem 0.65rem;
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  transition: var(--transition);
  white-space: nowrap;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--accent);
  background: rgba(226,176,74,0.08);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text);
  font-size: 1.5rem;
  cursor: pointer;
  padding: 0.25rem;
}

/* === Layout === */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 3rem 1.5rem 4rem;
  position: relative;
  z-index: 1;
}

.page-header {
  text-align: center;
  padding: 4rem 1.5rem 2rem;
  position: relative;
  z-index: 1;
}

.page-header h1 {
  font-family: var(--font-serif);
  font-size: clamp(2rem, 5vw, 3.2rem);
  color: var(--accent);
  line-height: 1.2;
  margin-bottom: 0.5rem;
  letter-spacing: -0.03em;
}

.page-header .subtitle {
  color: var(--text-muted);
  font-size: 1.1rem;
  max-width: 600px;
  margin: 0 auto;
}

/* === Hero (landing page) === */
.hero {
  text-align: center;
  padding: 6rem 1.5rem 4rem;
  position: relative;
  z-index: 1;
}

.hero-icon {
  font-size: 4rem;
  margin-bottom: 1.5rem;
  display: block;
  animation: float 4s ease-in-out infinite;
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-12px); }
}

.hero h1 {
  font-family: var(--font-serif);
  font-size: clamp(2.4rem, 6vw, 4rem);
  color: var(--accent);
  line-height: 1.15;
  margin-bottom: 1rem;
  letter-spacing: -0.04em;
}

.hero .tagline {
  font-size: 1.25rem;
  color: var(--text-muted);
  max-width: 580px;
  margin: 0 auto 2.5rem;
  line-height: 1.6;
}

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

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.7rem 1.5rem;
  border-radius: var(--radius);
  font-size: 0.95rem;
  font-weight: 600;
  text-decoration: none;
  transition: var(--transition);
  cursor: pointer;
  border: none;
  font-family: var(--font-sans);
}

.btn-primary {
  background: var(--accent);
  color: #0a0e17;
}

.btn-primary:hover {
  background: var(--accent-glow);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(226,176,74,0.25);
}

.btn-secondary {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border-light);
}

.btn-secondary:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: rgba(226,176,74,0.06);
}

/* === Section cards on landing === */
.section-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1.25rem;
  margin-top: 3rem;
}

.section-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  transition: var(--transition);
  text-decoration: none;
  color: var(--text);
  display: block;
}

.section-card:hover {
  border-color: var(--accent-dim);
  background: var(--bg-card-hover);
  transform: translateY(-3px);
  box-shadow: var(--shadow);
}

.section-card .card-icon {
  font-size: 1.6rem;
  margin-bottom: 0.75rem;
}

.section-card h3 {
  font-family: var(--font-serif);
  font-size: 1.1rem;
  color: var(--accent);
  margin-bottom: 0.4rem;
}

.section-card p {
  font-size: 0.88rem;
  color: var(--text-muted);
  line-height: 1.55;
}

/* === Content pages === */
.content-section {
  margin-bottom: 3rem;
}

.content-section h2 {
  font-family: var(--font-serif);
  font-size: 1.8rem;
  color: var(--accent);
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

.content-section h3 {
  font-family: var(--font-serif);
  font-size: 1.3rem;
  color: var(--text-heading);
  margin: 2rem 0 0.75rem;
}

.content-section h4 {
  font-size: 1.05rem;
  color: var(--text-heading);
  margin: 1.5rem 0 0.5rem;
}

.content-section p {
  margin-bottom: 1rem;
  color: var(--text);
}

.content-section ul, .content-section ol {
  margin: 0.75rem 0 1rem 1.5rem;
}

.content-section li {
  margin-bottom: 0.35rem;
}

.content-section strong {
  color: var(--text-heading);
}

/* === Cards within content === */
.info-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 1.25rem 0;
}

.info-card h4 {
  color: var(--accent);
  margin-top: 0;
}

/* === Definition blocks === */
.definition {
  background: rgba(96,165,250,0.06);
  border-left: 3px solid var(--blue);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 1rem 1.25rem;
  margin: 1.25rem 0;
}

.definition strong {
  color: var(--blue);
}

/* === Theorem blocks === */
.theorem {
  background: rgba(226,176,74,0.06);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 1rem 1.25rem;
  margin: 1.25rem 0;
}

.theorem .theorem-label {
  color: var(--accent);
  font-weight: 700;
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.4rem;
}

/* === Proof blocks === */
.proof {
  background: rgba(167,139,250,0.05);
  border-left: 3px solid var(--purple);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 1rem 1.25rem;
  margin: 1rem 0 1.25rem;
}

.proof summary {
  color: var(--purple);
  font-weight: 600;
  cursor: pointer;
  font-size: 0.9rem;
}

/* === Tables === */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.25rem 0;
  font-size: 0.9rem;
}

th {
  background: var(--bg-card);
  color: var(--accent);
  font-weight: 600;
  text-align: left;
  padding: 0.65rem 0.85rem;
  border-bottom: 2px solid var(--border-light);
}

td {
  padding: 0.55rem 0.85rem;
  border-bottom: 1px solid var(--border);
}

tr:hover td {
  background: rgba(226,176,74,0.03);
}

/* === Interactive Demos === */
.demo-container {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin: 1.5rem 0;
  overflow: hidden;
}

.demo-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--border);
  background: rgba(0,0,0,0.2);
}

.demo-header h4 {
  margin: 0;
  font-size: 0.9rem;
  color: var(--accent);
}

.demo-body {
  padding: 1rem;
}

.demo-controls {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-bottom: 1rem;
}

.demo-controls button {
  padding: 0.4rem 0.85rem;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--text);
  cursor: pointer;
  font-size: 0.82rem;
  transition: var(--transition);
  font-family: var(--font-sans);
}

.demo-controls button:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: rgba(226,176,74,0.08);
}

.demo-controls button.active {
  background: var(--accent);
  color: #0a0e17;
  border-color: var(--accent);
}

.demo-controls input[type="range"] {
  accent-color: var(--accent);
}

.demo-controls label {
  font-size: 0.82rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

/* === Tree Visualization === */
.tree-viz {
  display: flex;
  justify-content: center;
  padding: 1rem 0;
}

.tree-viz canvas {
  border-radius: var(--radius-sm);
}

.tree-info {
  text-align: center;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--text-muted);
  padding: 0.5rem;
}

.tree-info .highlight {
  color: var(--accent);
  font-weight: 600;
}

/* === Error Demo === */
.error-demo {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

@media (max-width: 600px) {
  .error-demo { grid-template-columns: 1fr; }
}

.error-track {
  background: rgba(0,0,0,0.2);
  border-radius: var(--radius-sm);
  padding: 0.75rem;
}

.error-track h5 {
  font-size: 0.85rem;
  color: var(--text-heading);
  margin-bottom: 0.5rem;
  text-align: center;
}

.error-track canvas {
  width: 100%;
  border-radius: 4px;
}

.error-stats {
  display: flex;
  justify-content: space-around;
  margin-top: 0.5rem;
  font-family: var(--font-mono);
  font-size: 0.78rem;
}

/* === Step indicator === */
.steps {
  display: flex;
  gap: 0.5rem;
  margin: 1rem 0;
  flex-wrap: wrap;
}

.step {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.82rem;
  color: var(--text-muted);
}

.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  font-size: 0.75rem;
  font-weight: 700;
}

/* === Code / Math === */
code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: rgba(255,255,255,0.06);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

pre {
  background: rgba(0,0,0,0.3);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1rem;
  overflow-x: auto;
  margin: 1rem 0;
  font-size: 0.85rem;
}

pre code {
  background: none;
  padding: 0;
}

/* === LaTeX display === */
.MathJax { font-size: 1.02em !important; }

mjx-container[display="true"] {
  margin: 1.25rem 0 !important;
  overflow-x: auto;
  overflow-y: hidden;
}

/* === Footer === */
footer {
  text-align: center;
  padding: 2rem 1.5rem;
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.82rem;
  position: relative;
  z-index: 1;
}

footer a {
  color: var(--accent);
  text-decoration: none;
}

/* === Highlight box === */
.highlight-box {
  background: rgba(226,176,74,0.06);
  border: 1px solid rgba(226,176,74,0.2);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
  text-align: center;
}

.highlight-box p {
  margin: 0;
  font-size: 1.05rem;
  color: var(--accent-glow);
}

/* === Tabs === */
.tabs {
  display: flex;
  gap: 0;
  border-bottom: 1px solid var(--border);
  margin-bottom: 1rem;
}

.tab-btn {
  padding: 0.5rem 1rem;
  border: none;
  background: none;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 500;
  border-bottom: 2px solid transparent;
  transition: var(--transition);
  font-family: var(--font-sans);
}

.tab-btn:hover { color: var(--text); }
.tab-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.tab-content { display: none; }
.tab-content.active { display: block; }

/* === Responsive === */
@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: absolute;
    top: 56px;
    left: 0;
    right: 0;
    background: rgba(10,14,23,0.95);
    backdrop-filter: blur(16px);
    flex-direction: column;
    padding: 0.5rem;
    border-bottom: 1px solid var(--border);
  }
  .nav-links.open { display: flex; }
  .nav-toggle { display: block; }

  .hero { padding: 3rem 1rem 2.5rem; }
  .hero h1 { font-size: 2rem; }

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

  .container { padding: 2rem 1rem 3rem; }
}