:root {
  --bg: #f4f7fb;
  --bg-hero: linear-gradient(145deg, #eef4ff 0%, #f8fafc 45%, #ecfeff 100%);
  --surface: #ffffff;
  --border: #dbe4f0;
  --text: #0f172a;
  --muted: #5b6b82;
  --accent: #0ea5e9;
  --accent-deep: #0369a1;
  --accent-soft: #e0f2fe;
  --violet: #6366f1;
  --violet-soft: #eef2ff;
  --slow: #ea580c;
  --slow-soft: #fff7ed;
  --fast: #059669;
  --fast-soft: #ecfdf5;
  --shadow: 0 4px 24px rgba(15, 23, 42, 0.06);
  --shadow-lg: 0 20px 50px rgba(14, 165, 233, 0.12);
  --font: "DM Sans", system-ui, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, monospace;
  --radius: 14px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
}

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

a:hover {
  color: var(--accent);
}

.container {
  width: min(1120px, 92vw);
  margin: 0 auto;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.85rem 0;
}

.logo {
  font-weight: 700;
  font-size: 1.2rem;
  color: var(--text);
  text-decoration: none;
}

.logo span {
  color: var(--accent);
}

nav {
  display: flex;
  gap: 1.1rem;
  align-items: center;
  flex-wrap: wrap;
}

nav a {
  color: var(--muted);
  font-size: 0.92rem;
  font-weight: 500;
}

nav a:hover {
  color: var(--text);
}

.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;
}

.lang-switcher select {
  font-family: var(--font);
  font-size: 0.85rem;
  padding: 0.35rem 0.5rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.55rem 1.15rem;
  border-radius: 10px;
  font-weight: 600;
  font-size: 0.92rem;
  text-decoration: none;
  transition: transform 0.15s, box-shadow 0.15s;
  border: none;
  cursor: pointer;
}

.btn:hover {
  transform: translateY(-2px);
  text-decoration: none;
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-deep) 100%);
  color: #fff;
  box-shadow: 0 4px 14px rgba(14, 165, 233, 0.35);
}

.btn-primary:hover {
  color: #fff;
  box-shadow: 0 8px 22px rgba(14, 165, 233, 0.4);
}

.btn-ghost {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
}

.section-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  background: var(--accent-soft);
  padding: 0.35rem 0.75rem;
  border-radius: 999px;
  margin-bottom: 0.75rem;
}

/* Hero */
.hero {
  background: var(--bg-hero);
  padding: 3.5rem 0 2rem;
  overflow: hidden;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2.5rem;
  align-items: center;
}

.hero h1 {
  font-size: clamp(2rem, 4.5vw, 2.85rem);
  line-height: 1.12;
  margin: 0 0 1rem;
  letter-spacing: -0.03em;
}

.hero .lead {
  font-size: 1.1rem;
  color: var(--muted);
  margin: 0 0 1.5rem;
  max-width: 520px;
}

.hero-actions {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 1.5rem;
}

.badges {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
}

.badges img {
  height: 22px;
}

.hero-visual {
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border);
  padding: 1rem;
}

.hero-visual svg {
  width: 100%;
  height: auto;
  display: block;
}

/* Sections */
section {
  padding: 4rem 0;
}

section.alt {
  background: var(--surface);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

h2 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  margin: 0 0 0.5rem;
  letter-spacing: -0.02em;
}

.section-intro {
  color: var(--muted);
  max-width: 640px;
  margin: 0 0 2rem;
  font-size: 1.05rem;
}

/* Diagram panels */
.diagram-panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  margin-bottom: 1.5rem;
}

.diagram-panel h3 {
  margin: 0 0 0.25rem;
  font-size: 1.1rem;
}

.diagram-panel .caption {
  color: var(--muted);
  font-size: 0.9rem;
  margin: 0 0 1rem;
}

.diagram-panel svg {
  width: 100%;
  height: auto;
  display: block;
}

.diagram-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
}

/* Concept cards */
.concept-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.25rem;
  margin-top: 2rem;
}

.concept-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  text-align: center;
  box-shadow: var(--shadow);
  transition: transform 0.2s, box-shadow 0.2s;
}

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

.concept-card .icon-wrap {
  width: 56px;
  height: 56px;
  margin: 0 auto 0.75rem;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.concept-card.slow .icon-wrap {
  background: var(--slow-soft);
  color: var(--slow);
}

.concept-card.proof .icon-wrap {
  background: var(--violet-soft);
  color: var(--violet);
}

.concept-card.fast .icon-wrap {
  background: var(--fast-soft);
  color: var(--fast);
}

.concept-card h3 {
  margin: 0 0 0.35rem;
  font-size: 1rem;
}

.concept-card p {
  margin: 0;
  font-size: 0.88rem;
  color: var(--muted);
}

/* Applications */
.app-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.25rem;
}

.app-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.35rem;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  align-items: start;
  box-shadow: var(--shadow);
  transition: border-color 0.2s, box-shadow 0.2s;
}

.app-card:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-lg);
}

.app-card svg {
  width: 48px;
  height: 48px;
  flex-shrink: 0;
}

.app-card h3 {
  margin: 0 0 0.35rem;
  font-size: 1.05rem;
}

.app-card p {
  margin: 0;
  font-size: 0.9rem;
  color: var(--muted);
}

/* Compare bar */
.compare-legend {
  display: flex;
  gap: 1.5rem;
  justify-content: center;
  margin-top: 1rem;
  font-size: 0.85rem;
  color: var(--muted);
}

.legend-dot {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  margin-right: 0.35rem;
  vertical-align: middle;
}

.legend-dot.slow { background: var(--slow); }
.legend-dot.fast { background: var(--fast); }

/* Features */
.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.25rem;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.35rem;
  box-shadow: var(--shadow);
}

.card h3 {
  margin: 0 0 0.5rem;
  color: var(--accent-deep);
  font-size: 1.05rem;
}

.card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.note {
  background: var(--slow-soft);
  border: 1px solid #fed7aa;
  border-radius: 10px;
  padding: 1rem 1.15rem;
  font-size: 0.92rem;
  color: var(--muted);
  margin-top: 1.5rem;
}

.note strong {
  color: var(--slow);
}

pre.code-block {
  background: #1e293b;
  color: #e2e8f0;
  border-radius: 10px;
  padding: 1.1rem 1.25rem;
  overflow-x: auto;
  margin: 0.75rem 0 0;
  font-family: var(--mono);
  font-size: 0.85rem;
  line-height: 1.5;
  box-shadow: var(--shadow);
}

.links-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 1.25rem;
}

.site-footer {
  padding: 2rem 0;
  text-align: center;
  color: var(--muted);
  font-size: 0.9rem;
  border-top: 1px solid var(--border);
  background: var(--surface);
}

/* Live demo */
.demo-layout {
  display: grid;
  grid-template-columns: minmax(280px, 340px) 1fr;
  gap: 1.5rem;
  align-items: start;
}

.demo-panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.35rem;
  box-shadow: var(--shadow);
}

.demo-panel h3 {
  margin: 0 0 1rem;
  font-size: 1.05rem;
}

.demo-field {
  display: block;
  margin-bottom: 1rem;
}

.demo-field > span {
  display: block;
  font-weight: 600;
  font-size: 0.9rem;
  margin-bottom: 0.35rem;
}

.demo-field small {
  display: block;
  color: var(--muted);
  font-size: 0.8rem;
  margin-top: 0.35rem;
  line-height: 1.4;
}

.demo-field select,
.demo-field input[type="text"] {
  width: 100%;
  padding: 0.5rem 0.65rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-family: var(--mono);
  font-size: 0.88rem;
  background: var(--bg);
}

.demo-input-row {
  display: flex;
  gap: 0.5rem;
}

.demo-input-row input {
  flex: 1;
}

.demo-run-btn {
  width: 100%;
  margin: 0.5rem 0 1rem;
  font-size: 1rem;
  padding: 0.75rem;
}

.demo-code-preview .code-block {
  margin: 0.35rem 0 0;
  font-size: 0.75rem;
  max-height: 140px;
}

.demo-code-label {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
}

.demo-steps {
  list-style: none;
  margin: 0;
  padding: 0;
}

.demo-step {
  display: flex;
  gap: 0.85rem;
  padding: 0.85rem 0;
  border-bottom: 1px solid var(--border);
  opacity: 0.55;
  transition: opacity 0.2s, background 0.2s;
}

.demo-step:last-child {
  border-bottom: none;
}

.demo-step.pending {
  opacity: 0.5;
}

.demo-step.active {
  opacity: 1;
  background: var(--accent-soft);
  margin: 0 -0.75rem;
  padding-left: 0.75rem;
  padding-right: 0.75rem;
  border-radius: 8px;
}

.demo-step.done {
  opacity: 1;
}

.demo-step.error {
  opacity: 1;
  background: #fef2f2;
}

.demo-step-slow.active .demo-step-num {
  background: var(--slow);
  animation: demo-pulse 1s ease-in-out infinite;
}

.demo-step-fast.done .demo-step-num {
  background: var(--fast);
}

@keyframes demo-pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.08); }
}

.demo-step-num {
  flex-shrink: 0;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--border);
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
}

.demo-step.active .demo-step-num,
.demo-step.done .demo-step-num {
  background: var(--accent);
  color: #fff;
}

.demo-step-body {
  flex: 1;
  min-width: 0;
}

.demo-step-body strong {
  display: block;
  font-size: 0.95rem;
}

.demo-step-body p {
  margin: 0.15rem 0 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.demo-step-detail {
  display: block;
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--accent-deep);
  margin-top: 0.35rem;
  word-break: break-all;
}

.demo-log-wrap {
  margin-top: 1.25rem;
}

.demo-log {
  background: #0f172a;
  color: #94a3b8;
  border-radius: 8px;
  padding: 0.75rem;
  font-family: var(--mono);
  font-size: 0.75rem;
  max-height: 160px;
  overflow-y: auto;
  margin-top: 0.35rem;
}

.demo-log-line {
  padding: 0.15rem 0;
  border-bottom: 1px solid #1e293b;
}

.demo-log-success {
  color: #6ee7b7;
}

.demo-log-error {
  color: #fca5a5;
}

.demo-compare {
  margin: 1rem 0;
}

.demo-compare-bar {
  display: flex;
  height: 36px;
  border-radius: 8px;
  overflow: hidden;
  border: 1px solid var(--border);
}

.demo-compare-solve {
  background: linear-gradient(90deg, #fb923c, #ea580c);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 600;
  min-width: 80px;
}

.demo-compare-verify {
  background: linear-gradient(90deg, #34d399, #059669);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 600;
  min-width: 72px;
}

.demo-compare-caption {
  font-size: 0.85rem;
  color: var(--muted);
  margin: 0.5rem 0 0;
  text-align: center;
}

@media (max-width: 900px) {
  .demo-layout {
    grid-template-columns: 1fr;
  }
  .hero-grid,
  .diagram-row,
  .concept-grid,
  .grid-3 {
    grid-template-columns: 1fr;
  }

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

  nav a:not(.btn) {
    display: none;
  }
}