:root {
  --bg: #F5F4F0;
  --surface: #FAFAF8;
  --surface2: #FFFFFF;
  --border: rgba(0,0,0,0.05);
  --border2: rgba(0,0,0,0.08);
  --border3: rgba(0,0,0,0.12);
  --black: #1A1A1A;
  --gray-100: #2D2D2D;
  --gray-300: #666;
  --gray-400: #888;
  --gray-500: #999;
  --gray-600: #AAA;
  --gray-700: #C4C0B8;
  --gray-800: #D8D5CE;
  --serif: 'Playfair Display', Georgia, serif;
  --mono: 'Geist Mono', 'SF Mono', monospace;
  --sans: 'DM Sans', system-ui, sans-serif;
}

*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { font-size: 15px; scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--black);
  font-family: var(--sans);
  font-weight: 300;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

::selection { background: rgba(0,0,0,0.08); }

/* Nav */
.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 48px;
  border-bottom: 1px solid var(--border);
  background: var(--surface);
  position: sticky;
  top: 0;
  z-index: 50;
}

.nav-logo {
  font-family: var(--sans);
  font-size: 15px;
  font-weight: 400;
  color: var(--gray-400);
  letter-spacing: 0.02em;
  text-decoration: none;
}

.nav-logo strong {
  color: var(--black);
  font-weight: 500;
}

.nav-right {
  display: flex;
  align-items: center;
  gap: 32px;
}

.nav-link {
  font-family: var(--sans);
  font-size: 13px;
  color: var(--gray-400);
  text-decoration: none;
  font-weight: 400;
  transition: color 0.15s;
}

.nav-link:hover { color: var(--gray-300); }

.nav-cta {
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  color: var(--surface);
  background: var(--black);
  border: none;
  padding: 9px 22px;
  border-radius: 6px;
  text-decoration: none;
  transition: opacity 0.15s;
}

.nav-cta:hover { opacity: 0.8; }

/* Container */
.container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 48px;
}

/* Hero */
.hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 120px 48px 100px;
  text-align: center;
}

.hero-eyebrow {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--gray-500);
  margin-bottom: 28px;
}

.hero h1 {
  font-family: var(--serif);
  font-size: 64px;
  font-weight: 400;
  line-height: 1.06;
  max-width: 640px;
  margin-bottom: 24px;
  letter-spacing: -0.01em;
}

.hero h1 em { font-style: italic; }

.hero-sub {
  font-size: 16px;
  color: var(--gray-400);
  max-width: 420px;
  line-height: 1.7;
  margin-bottom: 40px;
}

.hero-actions {
  display: flex;
  align-items: center;
  gap: 20px;
}

.hero-btn {
  font-family: var(--sans);
  font-size: 14px;
  font-weight: 500;
  padding: 13px 32px;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.15s;
  border: none;
  background: var(--black);
  color: var(--surface);
  text-decoration: none;
}

.hero-btn:hover { opacity: 0.8; }

.hero-link {
  font-family: var(--sans);
  font-size: 14px;
  color: var(--gray-400);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-color: var(--gray-700);
  transition: color 0.15s;
}

.hero-link:hover { color: var(--gray-300); }

/* Sections */
section {
  padding: 80px 48px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  align-items: center;
}

.section-label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--gray-500);
  margin-bottom: 16px;
}

.section-title {
  font-family: var(--serif);
  font-size: 36px;
  font-weight: 400;
  text-align: center;
  margin-bottom: 12px;
}

.section-sub {
  font-size: 14px;
  color: var(--gray-400);
  text-align: center;
  max-width: 420px;
  margin-bottom: 40px;
  line-height: 1.7;
}

/* Problem section */
.problem-text {
  max-width: 560px;
  text-align: center;
  font-size: 16px;
  color: var(--gray-300);
  line-height: 1.85;
}

.problem-text strong { color: var(--black); font-weight: 400; }

.problem-text code {
  font-family: var(--mono);
  font-size: 0.9em;
  color: var(--black);
  background: var(--surface);
  padding: 2px 6px;
  border: 1px solid var(--border2);
}

/* Terminal card */
.terminal-card {
  width: 100%;
  max-width: 860px;
  background: #111;
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid rgba(255,255,255,0.06);
}

.terminal-header {
  padding: 14px 20px;
  border-bottom: 1px solid rgba(255,255,255,0.06);
  display: flex;
  align-items: center;
  gap: 6px;
}

.td { width: 8px; height: 8px; border-radius: 50%; }
.td.r { background: #FF5F57; }
.td.y { background: #FFBD2E; }
.td.g { background: #28C840; }

.terminal-filename {
  font-family: var(--mono);
  font-size: 11px;
  color: rgba(255,255,255,0.3);
  margin-left: 10px;
}

.terminal-body {
  padding: 24px;
  font-family: var(--mono);
  font-size: 12px;
  line-height: 1.85;
  color: rgba(255,255,255,0.4);
  overflow-x: auto;
  white-space: pre;
}

.terminal-body .c { color: rgba(255,255,255,0.2); }
.terminal-body .k { color: #C4B89A; }
.terminal-body .s { color: #8BB88A; }
.terminal-body .h { color: rgba(255,255,255,0.7); }
.terminal-body .h2 { color: rgba(255,255,255,0.55); }

/* Three layers grid */
.layers-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1px;
  background: var(--border2);
  max-width: 960px;
  width: 100%;
  border: 1px solid var(--border2);
}

.layer-card {
  background: var(--surface);
  padding: 36px 32px;
}

.layer-num {
  font-family: var(--mono);
  font-size: 10px;
  color: var(--gray-600);
  margin-bottom: 16px;
}

.layer-title {
  font-family: var(--serif);
  font-size: 22px;
  font-weight: 400;
  margin-bottom: 10px;
}

.layer-desc {
  font-size: 13px;
  color: var(--gray-400);
  line-height: 1.65;
  margin-bottom: 20px;
}

.layer-sections {
  list-style: none;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--gray-500);
}

.layer-sections li {
  padding: 4px 0;
  border-top: 1px solid var(--border);
}

.layer-sections li:last-child { padding-bottom: 0; }

/* Steps grid */
.steps-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1px;
  background: var(--border2);
  max-width: 960px;
  width: 100%;
  border: 1px solid var(--border2);
}

.step-card {
  background: var(--surface);
  padding: 36px 32px;
}

.step-num {
  font-family: var(--mono);
  font-size: 10px;
  color: var(--gray-600);
  margin-bottom: 16px;
}

.step-title {
  font-family: var(--serif);
  font-size: 22px;
  font-weight: 400;
  margin-bottom: 10px;
}

.step-desc {
  font-size: 13px;
  color: var(--gray-400);
  line-height: 1.65;
  margin-bottom: 16px;
}

.step-code {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--black);
  background: var(--bg);
  border: 1px solid var(--border2);
  padding: 10px 14px;
}

/* Spec table */
.spec-table {
  width: 100%;
  max-width: 860px;
}

.spec-group-label {
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--gray-500);
  padding: 20px 0 10px;
}

.spec-row {
  display: grid;
  grid-template-columns: 1fr 1fr auto;
  gap: 16px;
  padding: 12px 0;
  border-top: 1px solid var(--border);
  align-items: baseline;
  font-size: 13px;
}

.spec-name {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--black);
}

.spec-desc {
  color: var(--gray-400);
  font-size: 12px;
}

.spec-badge {
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.04em;
  color: var(--gray-500);
  border: 1px solid var(--border2);
  padding: 3px 8px;
  background: var(--surface);
}

.spec-badge.optional { color: var(--gray-600); }

/* Footer */
footer {
  padding: 48px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.footer-left {
  font-size: 12px;
  color: var(--gray-500);
}

.footer-links {
  display: flex;
  gap: 24px;
}

.footer-links a {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--gray-500);
  text-decoration: none;
  transition: color 0.15s;
}

.footer-links a:hover { color: var(--gray-300); }

/* Responsive */
@media (max-width: 768px) {
  .nav { padding: 16px 24px; }
  .nav-right { gap: 16px; }
  .hero { padding: 80px 24px 60px; }
  .hero h1 { font-size: 40px; }
  section { padding: 60px 24px; }
  .layers-grid,
  .steps-grid { grid-template-columns: 1fr; }
  .container { padding: 0 24px; }
  footer { padding: 32px 24px; flex-direction: column; gap: 16px; text-align: center; }
  .spec-row { grid-template-columns: 1fr; gap: 4px; }
}