/* The Nonlinearity Index — plain CSS, no framework. */

:root {
  --bg: #121212;
  --bg-2: #181818;
  --card: #161616;
  --ink: #ececec;
  --muted: #9a9a9a;
  --faint: #6b6b6b;
  --line: #262626;
  --line-2: #333;
  --acc: #8b96ff;
  --acc-soft: rgba(139, 150, 255, .12);
  --grid: #222;
  --c1: #f0b35e;
  --c2: #6fd3b0;
  --sans: Geist, ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
  --mono: "Geist Mono", ui-monospace, "SF Mono", Menlo, monospace;
  --math: "STIX Two Text", "Cambria Math", "Times New Roman", serif;
  color-scheme: dark;
}
:root[data-theme="light"] {
  --bg: #fbfbfa;
  --bg-2: #f3f3f1;
  --card: #ffffff;
  --ink: #161616;
  --muted: #5d5d5d;
  --faint: #8a8a8a;
  --line: #e6e6e3;
  --line-2: #d6d6d2;
  --acc: #4150d8;
  --acc-soft: rgba(65, 80, 216, .09);
  --grid: #efefec;
  --c1: #c2700a;
  --c2: #1c8a66;
  color-scheme: light;
}
@media (prefers-color-scheme: light) {
  :root:not([data-theme="dark"]) {
    --bg: #fbfbfa;
    --bg-2: #f3f3f1;
    --card: #ffffff;
    --ink: #161616;
    --muted: #5d5d5d;
    --faint: #8a8a8a;
    --line: #e6e6e3;
    --line-2: #d6d6d2;
    --acc: #4150d8;
    --acc-soft: rgba(65, 80, 216, .09);
    --grid: #efefec;
    --c1: #c2700a;
    --c2: #1c8a66;
    color-scheme: light;
  }
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 220px; -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 15px/1.65 var(--sans); -webkit-font-smoothing: antialiased; }
a { color: inherit; text-decoration-color: var(--line-2); text-underline-offset: 3px; }
a:hover { color: var(--acc); text-decoration-color: currentColor; }
h1, h2, h3, h4 { font-weight: 600; letter-spacing: -.015em; line-height: 1.2; margin: 0; }
p { margin: 0; }
button { font: inherit; color: inherit; cursor: pointer; }
:focus-visible { outline: 2px solid var(--acc); outline-offset: 2px; border-radius: 4px; }
main, .site { max-width: 1240px; margin: 0 auto; padding-left: 40px; padding-right: 40px; }

/* ---------------------------------------------------------------- header / footer */
header.site {
  position: sticky; top: 0; z-index: 10; display: flex; align-items: center; justify-content: space-between; gap: 16px;
  height: 64px; max-width: none; background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(12px); -webkit-backdrop-filter: blur(12px); border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; font-weight: 600; font-size: 15px; white-space: nowrap; }
.brand svg { width: 24px; height: 24px; color: var(--ink); }
header.site nav { display: flex; align-items: center; gap: 26px; font-size: 14px; }
header.site nav a { text-decoration: none; color: var(--muted); white-space: nowrap; }
header.site nav a:hover, header.site nav a[aria-current="page"] { color: var(--ink); }
.gh { display: inline-flex; align-items: center; gap: 7px; padding: 6px 12px; border: 1px solid var(--line-2); border-radius: 999px; color: var(--ink) !important; text-decoration: none; font-size: 13px; white-space: nowrap; }
.gh:hover { border-color: var(--acc); }
.gh svg { width: 15px; height: 15px; }
.star-cta { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; margin-top: 26px; color: var(--muted); font-size: 14px; }
footer.site .star a { color: var(--acc); text-decoration: none; }
.theme { width: 34px; height: 34px; border-radius: 50%; border: 1px solid var(--line-2); background: var(--bg-2); font-size: 15px; line-height: 1; }
footer.site { border-top: 1px solid var(--line); margin-top: 96px; padding-top: 28px; padding-bottom: 48px; color: var(--faint); font-size: 13px; display: grid; gap: 4px; max-width: none; }
footer.site p { max-width: 1160px; margin: 0 auto; width: 100%; }

/* ---------------------------------------------------------------- hero */
.hero { padding: 96px 0 56px; border-bottom: 1px solid var(--line); }
.eyebrow { font: 500 12px var(--mono); letter-spacing: .14em; text-transform: uppercase; color: var(--muted); }
.hero h1 { font-size: clamp(34px, 5vw, 56px); margin: 22px 0 28px; letter-spacing: -.025em; }
.hero h1.eq { font: 400 clamp(48px, 9vw, 112px)/1 var(--math); letter-spacing: 0; }
.phi { color: var(--acc); font-family: var(--math); font-style: italic; }
.hero-copy { max-width: 720px; display: grid; gap: 14px; color: var(--muted); font-size: 16.5px; }
.hero-copy .big { color: var(--ink); font-size: clamp(19px, 2.2vw, 23px); line-height: 1.45; letter-spacing: -.01em; }
.progress { margin-top: 40px; max-width: 520px; }
.progress .bar { height: 4px; border-radius: 4px; background: var(--line); overflow: hidden; }
.progress .bar span { display: block; height: 100%; background: var(--acc); border-radius: 4px; }
.progress p { margin-top: 10px; font: 13px var(--mono); color: var(--muted); }
.progress strong { color: var(--ink); font-weight: 500; }

/* ---------------------------------------------------------------- controls */
.controls { display: none; position: sticky; top: 64px; z-index: 5; padding: 16px 0 14px; background: var(--bg); border-bottom: 1px solid var(--line); }
.js .controls { display: grid; gap: 12px; }
.controls .row { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; justify-content: space-between; }
#q { flex: 1 1 320px; min-width: 0; padding: 10px 14px; border-radius: 10px; border: 1px solid var(--line-2); background: var(--bg-2); color: var(--ink); font: 14px var(--sans); }
#q::placeholder { color: var(--faint); }
#q:focus { outline: none; border-color: var(--acc); }
.seg { display: inline-flex; padding: 3px; border-radius: 10px; background: var(--bg-2); border: 1px solid var(--line); flex-wrap: wrap; }
.seg button { border: 0; background: none; padding: 6px 12px; border-radius: 7px; font-size: 13px; color: var(--muted); }
.seg button[aria-pressed="true"] { background: var(--card); color: var(--ink); box-shadow: 0 0 0 1px var(--line-2); }
.toggles { display: flex; gap: 6px; flex-wrap: wrap; }
.toggles button { border: 1px solid var(--line-2); background: none; padding: 5px 11px; border-radius: 999px; font-size: 12.5px; color: var(--muted); }
.toggles button[aria-pressed="true"] { border-color: var(--acc); color: var(--acc); background: var(--acc-soft); }
.shown { font: 12.5px var(--mono); color: var(--faint); white-space: nowrap; }

.families { display: flex; flex-wrap: wrap; gap: 6px 18px; padding: 22px 0 6px; font-size: 13px; }
.families a { color: var(--muted); text-decoration: none; }
.families a:hover { color: var(--acc); }
.families span { font-family: var(--mono); color: var(--faint); font-size: 11.5px; }

/* ---------------------------------------------------------------- tiers & families */
.tier { padding-top: 56px; }
.tier-head { display: grid; grid-template-columns: 64px 1fr auto; gap: 20px; align-items: start; padding-bottom: 8px; }
.tier-head .num { font: italic 400 40px/1 var(--math); color: var(--acc); }
.tier-head h2 { font-size: 30px; }
.tier-head p { color: var(--muted); max-width: 640px; margin-top: 8px; }
.count { font: 12px var(--mono); color: var(--faint); white-space: nowrap; padding-top: 6px; }
.family { padding-top: 34px; }
.fam-head { display: flex; align-items: baseline; gap: 12px; padding-top: 18px; border-top: 1px solid var(--line); }
.fam-head h3 { font-size: 19px; }
.lead { color: var(--muted); margin: 6px 0 18px; max-width: 720px; }

.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(268px, 1fr)); gap: 14px; }
.fn {
  display: flex; flex-direction: column; gap: 10px; padding: 16px 16px 14px; border: 1px solid var(--line); border-radius: 14px;
  background: var(--card); transition: border-color .15s;
}
.fn:hover, .fn:target { border-color: var(--line-2); }
.fn:target { box-shadow: 0 0 0 1px var(--acc); }
.fn header h4 { font-size: 16px; }
.fn header h4 a { text-decoration: none; }
.aka { color: var(--faint); font-size: 12.5px; margin-top: 2px; }
.fn figure { margin: 0; }
.fn figcaption, .legend { line-height: 1.5; font: 11.5px var(--mono); color: var(--faint); margin-top: 4px; display: flex; gap: 12px; flex-wrap: wrap; }
.legend .k0::before, .legend .k1::before, .legend .k2::before { content: ""; display: inline-block; width: 12px; height: 2px; margin-right: 5px; vertical-align: 3px; background: var(--acc); }
.legend .k1::before { background: var(--c1); }
.legend .k2::before { background: var(--c2); }

svg.plot { display: block; width: 100%; height: auto; aspect-ratio: 200 / 120; background: var(--bg-2); border-radius: 9px; }
svg .g { stroke: var(--grid); stroke-width: .6; }
svg .ax { stroke: var(--line-2); stroke-width: .9; }
svg .c { fill: none; stroke: var(--acc); stroke-width: 1.9; stroke-linejoin: round; stroke-linecap: round; }
svg .c1 { stroke: var(--c1); }
svg .c2 { stroke: var(--c2); }
svg .d { fill: none; stroke: var(--muted); stroke-width: 1.1; stroke-dasharray: 3 2.5; opacity: .8; }
svg .t { font: 7.5px var(--mono); fill: var(--faint); }
svg.spark { width: 64px; height: 26px; display: block; }
svg.spark .c { stroke-width: 1.6; }

.formula { font: 17px/1.5 var(--math); color: var(--ink); padding: 8px 0 4px; overflow-wrap: anywhere; }
.formula .cases span { white-space: nowrap; }
.formula i { font-style: italic; }
.formula sup, .formula sub { font-size: .68em; }
.formula.pw { display: flex; align-items: center; gap: 8px; font-size: 15.5px; }
.formula .cases { display: grid; grid-template-columns: auto auto; gap: 1px 14px; padding-left: 10px; border-left: 1.5px solid var(--muted); border-radius: 6px 0 0 6px; }
.formula .if { color: var(--muted); }
.formula .lhs { white-space: nowrap; }
.desc { color: var(--muted); font-size: 13.8px; line-height: 1.6; }
.tags { list-style: none; padding: 0; margin: 2px 0 0; display: flex; flex-wrap: wrap; gap: 5px; }
.tags li { font: 11.5px var(--mono); padding: 2px 8px; border-radius: 999px; border: 1px solid var(--line-2); color: var(--muted); }
.tags li sup { font-size: .75em; }
.tags .torch { color: var(--acc); border-color: color-mix(in srgb, var(--acc) 45%, transparent); }
.src { font-size: 12px; color: var(--faint); }
.seen { font-size: 12.5px; color: var(--muted); margin-top: auto; padding-top: 8px; border-top: 1px dashed var(--line); }
.seen span { font: 11px var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--faint); margin-right: 4px; }

.empty { padding: 60px 0; text-align: center; color: var(--muted); }

/* ---------------------------------------------------------------- tables & blocks */
.block { padding-top: 80px; }
.block h2 { font-size: 26px; }
.tbl { overflow-x: auto; border: 1px solid var(--line); border-radius: 12px; }
table { width: 100%; border-collapse: collapse; font-size: 13.5px; }
th, td { text-align: left; padding: 8px 12px; border-bottom: 1px solid var(--line); vertical-align: middle; }
tbody tr:last-child td { border-bottom: 0; }
th { font: 500 11px var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--faint); background: var(--bg-2); position: sticky; top: 0; }
td:first-child a { text-decoration: none; font-weight: 500; }
td { color: var(--muted); }
td:first-child { color: var(--ink); }
.queue { list-style: none; padding: 0; margin: 0; display: flex; flex-wrap: wrap; gap: 8px; }
.queue li { padding: 6px 12px; border: 1px dashed var(--line-2); border-radius: 999px; font-size: 13px; color: var(--muted); }
.about .cols { display: grid; grid-template-columns: repeat(3, 1fr); gap: 32px; margin-top: 20px; }
.about h3 { font-size: 15px; margin-bottom: 8px; }
.about p { color: var(--muted); font-size: 14px; }
.about b { color: var(--ink); font-weight: 500; }

/* ---------------------------------------------------------------- use cases */
.ucgrid { display: grid; grid-template-columns: repeat(auto-fill, minmax(360px, 1fr)); gap: 16px; padding-top: 28px; }
.uc { display: flex; flex-direction: column; gap: 10px; padding: 22px; border: 1px solid var(--line); border-radius: 14px; background: var(--card); }
.uc:target { box-shadow: 0 0 0 1px var(--acc); }
.uc .area { font: 500 11px var(--mono); letter-spacing: .12em; text-transform: uppercase; color: var(--acc); }
.uc h3 { font-size: 19px; }
.uc h3 a { text-decoration: none; }
.uc .arch { color: var(--faint); font-size: 13px; margin-top: -4px; }
.uc h4 { font: 500 11px var(--mono); letter-spacing: .1em; text-transform: uppercase; color: var(--faint); margin-top: 6px; }
.picks { list-style: none; padding: 0; margin: 0; display: grid; gap: 4px; }
.picks li { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.fchip { display: inline-flex; align-items: center; gap: 8px; padding: 2px 10px 2px 3px; border: 1px solid var(--line-2); border-radius: 9px; text-decoration: none; background: var(--bg-2); }
.fchip:hover { border-color: var(--acc); }
.fchip svg.spark { width: 46px; height: 20px; }
.fchip .nm { font-size: 13.5px; font-weight: 500; color: var(--ink); }
.picks .role { font-size: 12.5px; color: var(--muted); }
.uc .why { color: var(--muted); font-size: 14px; }
.uc .caveat { font-size: 13.5px; color: var(--muted); padding: 10px 12px; border-radius: 9px; background: var(--bg-2); }
.uc .caveat strong { color: var(--ink); font-weight: 500; }
.uc .ex { font: 12px var(--mono); color: var(--faint); margin-top: auto; padding-top: 8px; border-top: 1px dashed var(--line); }
.seg.wrap { flex-wrap: wrap; }
table.matrix th:not(:first-child), table.matrix td:not(:first-child) { text-align: center; padding: 8px 6px; }
table.matrix th:not(:first-child) span { writing-mode: vertical-rl; transform: rotate(180deg); display: inline-block; max-height: 150px; text-transform: none; letter-spacing: 0; font-size: 11.5px; }
table.matrix td:not(:first-child) { color: var(--acc); }
table.matrix tr.dim td { opacity: .25; }

/* ---------------------------------------------------------------- responsive */
@media (max-width: 900px) {
  main, .site { padding-left: 20px; padding-right: 20px; }
  .about .cols { grid-template-columns: 1fr; }
  .tier-head { grid-template-columns: 44px 1fr; }
  .tier-head .count { display: none; }
  .ucgrid { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  main, .site { padding-left: 16px; padding-right: 16px; }
  header.site nav { gap: 14px; }
  header.site nav a[href$="#about"] { display: none; }
  .brand span { font-size: 13.5px; }
  .brand { gap: 7px; }
  header.site { gap: 10px; }
  header.site nav { gap: 12px; font-size: 13.5px; }
  header.site nav .gh { padding: 7px; }
  header.site nav .gh span { display: none; }
  .hero { padding: 56px 0 40px; }
  .controls { position: static; }
  html { scroll-padding-top: 80px; }
  .grid { grid-template-columns: 1fr; }
  .uc { padding: 18px; }
}
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }