:root {
  --paper: #fafafa;
  --ink: #1c1c1c;
  --muted: #5f6368;
  --line: #d8d8d8;
  --slate: #2f3a4a;
  --slate-soft: #e9edf1;
  --amber: #9a6e27;
  --max: 1180px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: Inter, system-ui, sans-serif;
  line-height: 1.7;
  font-size: 15px;
}
a { color: inherit; }
a:focus-visible, button:focus-visible { outline: 2px solid var(--slate); outline-offset: 4px; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  border-bottom: 1px solid var(--line);
  background: rgba(250, 250, 250, .96);
  backdrop-filter: blur(8px);
}
.nav-wrap {
  max-width: var(--max);
  margin: auto;
  min-height: 58px;
  padding: 0 28px;
  display: flex;
  align-items: center;
  gap: 38px;
}
.wordmark {
  font: 600 21px/1 "IBM Plex Sans", sans-serif;
  letter-spacing: -.05em;
  text-decoration: none;
  white-space: nowrap;
}
.nav-toggle {
  display: none;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--ink);
  padding: 5px 9px;
  font: inherit;
}
.nav-links { display: flex; align-items: center; flex-wrap: wrap; gap: 23px; }
.nav-links a {
  color: var(--muted);
  text-decoration: none;
  font-size: 13px;
  white-space: nowrap;
}
.nav-links a:hover, .nav-links a.active { color: var(--ink); }
.nav-links a.active { border-bottom: 1px solid var(--slate); }

.page { max-width: var(--max); margin: auto; padding: 72px 28px 96px; }
.eyebrow {
  color: var(--muted);
  font-size: 12px;
  letter-spacing: .13em;
  text-transform: uppercase;
  margin: 0 0 22px;
}
h1, h2, h3 { font-family: "IBM Plex Sans", sans-serif; font-weight: 500; line-height: 1.2; letter-spacing: -.035em; }
h1 { font-size: clamp(44px, 7vw, 82px); max-width: 710px; margin: 0 0 38px; }
h2 { font-size: clamp(25px, 3vw, 36px); margin: 0 0 22px; }
h3 { font-size: 20px; margin: 0 0 10px; }
p { max-width: 720px; margin: 0 0 20px; }
.lede { font: 400 20px/1.65 Georgia, serif; max-width: 650px; }
.small { color: var(--muted); font-size: 13px; }
.rule { height: 1px; background: var(--line); margin: 64px 0; }

.hero { display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(280px, .95fr); gap: 54px; align-items: center; min-height: 540px; }
.hero h1 { font: 600 clamp(48px, 7vw, 82px)/.99 Georgia, serif; letter-spacing: -.045em; }
.hero-copy { padding-bottom: 20px; }
.hero-actions { display: flex; gap: 22px; margin-top: 34px; flex-wrap: wrap; }
.text-link { color: var(--slate); font-size: 14px; text-underline-offset: 4px; }
.model-figure { width: 100%; max-width: 470px; justify-self: end; color: #d8d8d8; }
.model-figure circle { fill: var(--paper); stroke: #d4d4d4; stroke-width: 1.4; }
.model-figure line, .model-figure path { stroke: #cfcfcf; stroke-width: 1.4; fill: none; }
.model-figure text { fill: #cfcfcf; font: 12px Inter, sans-serif; text-anchor: middle; }

.section-intro { display: grid; grid-template-columns: .8fr 1.2fr; gap: 44px; align-items: start; }
.section-intro > h2 { font-size: 28px; }
.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px; margin-top: 36px; }
.feature { border-top: 1px solid var(--ink); padding-top: 17px; }
.feature-number { font: 500 14px "IBM Plex Sans", sans-serif; color: var(--slate); margin-bottom: 26px; }
.feature p { color: var(--muted); font-size: 14px; }
.component-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 0 36px; margin-top: 32px; border-top: 1px solid var(--line); }
.component { display: block; padding: 20px 0; border-bottom: 1px solid var(--line); text-decoration: none; }
.component:hover h3 { color: var(--slate); }
.component h3 { font-size: 18px; margin-bottom: 4px; }
.component p { color: var(--muted); font-size: 13px; margin: 0; }
.cta-line { display: flex; gap: 24px; flex-wrap: wrap; margin-top: 25px; }

.page-head { border-bottom: 1px solid var(--line); padding-bottom: 40px; margin-bottom: 48px; }
.page-head h1 { font: 500 clamp(40px, 6vw, 68px)/1.05 Georgia, serif; max-width: 800px; margin-bottom: 24px; }
.content-grid { display: grid; grid-template-columns: 220px minmax(0, 720px); gap: 52px; align-items: start; }
.side-index { position: sticky; top: 86px; border-top: 1px solid var(--ink); padding-top: 12px; }
.side-index a { display: block; color: var(--muted); text-decoration: none; font-size: 13px; margin: 5px 0; }
.side-index a:hover { color: var(--ink); }
.content h2 { margin-top: 48px; padding-top: 20px; border-top: 1px solid var(--line); }
.content h2:first-child { margin-top: 0; border-top: 0; padding-top: 0; }
.content h3 { margin-top: 28px; }
.content ul { padding-left: 20px; margin-top: 8px; }
.content li { margin: 5px 0; }
.callout { border-left: 3px solid var(--slate); padding: 4px 0 4px 20px; margin: 28px 0; color: var(--muted); }
.caution { border-left-color: var(--amber); }
.equation { border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); padding: 24px 10px; margin: 25px 0; font: 20px/1.5 Georgia, serif; text-align: center; overflow-x: auto; }
.table-wrap { overflow-x: auto; margin: 25px 0; }
table { width: 100%; border-collapse: collapse; font-size: 13px; min-width: 560px; }
th, td { border-bottom: 1px solid var(--line); padding: 12px 10px; text-align: left; vertical-align: top; }
th { border-top: 1px solid var(--ink); font: 500 12px "IBM Plex Sans", sans-serif; letter-spacing: .06em; text-transform: uppercase; }
.directory { border: 1px solid var(--line); padding: 20px; font: 13px/1.8 ui-monospace, SFMono-Regular, Consolas, monospace; background: #f4f4f4; overflow-x: auto; }
.stat-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; margin: 28px 0; }
.stat { border-top: 1px solid var(--ink); padding-top: 12px; }
.stat strong { display: block; font: 500 27px "IBM Plex Sans", sans-serif; }
.stat span { color: var(--muted); font-size: 12px; }
.author-grid { display: grid; grid-template-columns: 210px 1fr; gap: 38px; align-items: start; }
.author-mark { aspect-ratio: 1; border: 1px solid var(--line); display: grid; place-items: center; color: var(--muted); font: 36px Georgia, serif; }

.site-footer { border-top: 1px solid var(--line); padding: 44px 28px 54px; }
.footer-inner { max-width: var(--max); margin: auto; display: grid; grid-template-columns: 1.3fr 1fr 1fr 1fr; gap: 28px; }
.footer-inner h3 { font-size: 13px; letter-spacing: .08em; text-transform: uppercase; margin-bottom: 10px; }
.footer-inner a { display: block; color: var(--muted); font-size: 13px; text-decoration: none; margin: 4px 0; }
.footer-inner a:hover { color: var(--ink); }
.copyright { max-width: var(--max); margin: 40px auto 0; color: var(--muted); font-size: 12px; }

@media (max-width: 920px) {
  .nav-wrap { gap: 18px; padding: 0 20px; }
  .nav-toggle { display: block; margin-left: auto; }
  .nav-links { display: none; position: absolute; top: 58px; left: 0; right: 0; padding: 16px 20px 22px; background: var(--paper); border-bottom: 1px solid var(--line); gap: 9px 18px; }
  .nav-links.open { display: flex; }
  .hero { grid-template-columns: 1fr; gap: 20px; min-height: 0; }
  .model-figure { justify-self: start; max-width: 420px; order: -1; }
  .content-grid { grid-template-columns: 1fr; gap: 28px; }
  .side-index { position: static; display: flex; gap: 16px; flex-wrap: wrap; }
}
@media (max-width: 620px) {
  body { font-size: 14px; }
  .page { padding: 48px 20px 68px; }
  .hero h1 { font-size: clamp(43px, 14vw, 66px); }
  .lede { font-size: 18px; }
  .feature-grid, .component-grid, .stat-grid, .footer-inner, .author-grid { grid-template-columns: 1fr; }
  .section-intro { grid-template-columns: 1fr; gap: 8px; }
  .rule { margin: 42px 0; }
  .site-footer { padding-left: 20px; padding-right: 20px; }
  .footer-inner { gap: 24px; }
}