:root {
  --four-ink: #17212b;
  --four-paper: #f7f4ee;
  --four-surface: #fffdf8;
  --four-line: #b9b0a4;
  --four-muted: #625f59;
  --four-blue: #164b78;
  --four-red: #9b332d;
  --four-max: 70rem;
}

* { box-sizing: border-box; }
html { color-scheme: light; }
body {
  margin: 0;
  color: var(--four-ink);
  background:
    radial-gradient(circle at 86% 0%, rgba(22, 75, 120, .1), transparent 24rem),
    var(--four-paper);
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.58;
}
a { color: inherit; text-decoration-thickness: 1px; text-underline-offset: .16em; }
a:hover { color: var(--four-blue); }
.skip-link { position: absolute; left: -9999px; top: .75rem; z-index: 10; padding: .5rem .75rem; background: var(--four-ink); color: white; }
.skip-link:focus { left: .75rem; }
.site-header {
  position: sticky;
  top: 0;
  z-index: 4;
  border-bottom: 1px solid var(--four-ink);
  background: color-mix(in srgb, var(--four-surface) 94%, transparent);
  backdrop-filter: blur(14px);
}
.header-inner {
  display: grid;
  gap: .75rem;
  width: min(var(--four-max), calc(100% - 2rem));
  margin: auto;
  padding: .85rem 0 .72rem;
}
.brand { font-size: .74rem; font-weight: 760; letter-spacing: .08em; text-decoration: none; text-transform: uppercase; }
.primary-nav { display: flex; flex-wrap: wrap; gap: .9rem; font-size: .74rem; letter-spacing: .04em; text-transform: uppercase; }
.primary-nav a { padding: .22rem 0; text-decoration: none; }
.primary-nav a[aria-current="page"] { color: var(--four-red); border-bottom: 2px solid var(--four-red); }
.paper-main { width: min(var(--four-max), calc(100% - 2rem)); margin: auto; }
.paper-hero { display: grid; gap: 2rem; padding: clamp(3rem, 8vw, 6.5rem) 0 clamp(2.5rem, 6vw, 4rem); border-bottom: 1px solid var(--four-line); }
.eyebrow { margin: 0 0 .8rem; color: var(--four-red); font-size: .75rem; font-weight: 760; letter-spacing: .11em; text-transform: uppercase; }
h1, h2, h3 { margin: 0; color: var(--four-ink); font-family: ui-serif, Georgia, Cambria, "Times New Roman", serif; line-height: 1.06; }
h1 { max-width: 13ch; font-size: clamp(2.65rem, 8vw, 5.6rem); font-weight: 530; letter-spacing: -.045em; }
h2 { font-size: clamp(1.5rem, 3.4vw, 2.45rem); letter-spacing: -.025em; }
h3 { font-size: 1.07rem; }
.subtitle { max-width: 38rem; margin: 1.1rem 0 0; color: var(--four-muted); font-family: ui-serif, Georgia, Cambria, "Times New Roman", serif; font-size: clamp(1.18rem, 2.5vw, 1.55rem); line-height: 1.34; }
.meta { display: flex; flex-wrap: wrap; gap: .5rem 1rem; margin: 1.25rem 0 0; color: var(--four-muted); font-size: .88rem; }
.meta span + span::before { content: "·"; margin-right: 1rem; color: var(--four-line); }
.cover-panel { align-self: end; max-width: 19rem; padding: .85rem; border: 1px solid var(--four-line); background: var(--four-surface); }
.cover-panel img { display: block; width: 100%; height: auto; }
.section { padding: clamp(2.6rem, 6vw, 4.8rem) 0; border-bottom: 1px solid var(--four-line); }
.section > p { max-width: 52rem; }
.abstract { max-width: 56rem; color: var(--four-muted); font-size: 1.05rem; }
.equation { overflow-x: auto; max-width: 56rem; margin: 1.25rem 0 0; padding: 1rem 1.15rem; border-left: .3rem solid var(--four-blue); background: var(--four-surface); font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: clamp(.86rem, 2vw, 1rem); white-space: pre-wrap; }
.record-grid { display: grid; gap: 1rem; grid-template-columns: repeat(auto-fit, minmax(min(100%, 14rem), 1fr)); margin-top: 1.5rem; }
.record { min-height: 100%; padding: 1.1rem; border: 1px solid var(--four-line); background: var(--four-surface); }
.record .label { display: block; margin-bottom: .45rem; color: var(--four-blue); font-size: .7rem; font-weight: 760; letter-spacing: .09em; text-transform: uppercase; }
.record p { margin: 0; color: var(--four-muted); }
.action-row { display: flex; flex-wrap: wrap; gap: .7rem; margin-top: 1.5rem; }
.button { display: inline-block; padding: .64rem .82rem; border: 1px solid var(--four-ink); background: var(--four-ink); color: white; font-size: .77rem; font-weight: 760; letter-spacing: .06em; text-decoration: none; text-transform: uppercase; }
.button.secondary { background: transparent; color: var(--four-ink); }
.boundary { max-width: 56rem; padding: 1rem 1.15rem; border: 1px solid var(--four-line); background: rgba(255, 253, 248, .7); color: var(--four-muted); }
.boundary strong { color: var(--four-ink); }
.source-list { max-width: 54rem; padding-left: 1.15rem; }
.source-list li + li { margin-top: .55rem; }
.paper-footer { width: min(var(--four-max), calc(100% - 2rem)); margin: auto; padding: 2rem 0 3rem; color: var(--four-muted); font-size: .83rem; }
.paper-footer nav { display: flex; flex-wrap: wrap; gap: .8rem; margin-top: .75rem; }
@media (min-width: 48rem) {
  .header-inner { grid-template-columns: 1fr auto; align-items: center; }
  .primary-nav { justify-content: flex-end; }
  .paper-hero { grid-template-columns: 1fr minmax(12rem, 19rem); align-items: end; }
}