/* ==========================================================================
   GTOI — redesigned.  Single stylesheet, design tokens first.
   ========================================================================== */

/* ---------- 1. tokens ---------- */
:root {
  --font-ui: "Inter", ui-sans-serif, system-ui, -apple-system, "Segoe UI",
    Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-display: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua",
    Georgia, serif;
  --font-mono: ui-monospace, "JetBrains Mono", "SF Mono", "Cascadia Mono",
    Menlo, Consolas, "Liberation Mono", monospace;
  --fig-font: var(--font-ui);

  --r-sm: 6px;
  --r: 12px;
  --r-lg: 18px;
  --shadow-1: 0 1px 2px rgba(10, 15, 30, .06), 0 1px 1px rgba(10, 15, 30, .04);
  --shadow-2: 0 10px 30px -12px rgba(10, 15, 30, .18), 0 2px 6px rgba(10, 15, 30, .05);
  --shadow-3: 0 30px 60px -24px rgba(10, 15, 30, .3);
  --maxw: 74ch;
  --ease: cubic-bezier(.22, .61, .36, 1);
  --dur: .22s;
  --lh: 1.72;
  --fs: 17px;
}

:root[data-width="wide"] { --maxw: 92ch; }
:root[data-width="full"] { --maxw: min(1320px, 100%); }
:root[data-font="sm"] { --fs: 15.5px; }
:root[data-font="lg"] { --fs: 18.5px; }

:root,
:root[data-theme="light"] {
  --bg: #f7f8fb;
  --bg-2: #eef1f7;
  --panel: #ffffff;
  --panel-2: #f4f6fa;
  --panel-3: #e9edf5;
  --line: #e0e5ee;
  --line-2: #ccd4e2;
  --ink: #131722;
  --ink-2: #46506a;
  --ink-3: #6b7793;
  --accent: #3f51ff;
  --accent-ink: #ffffff;
  --accent-soft: #eceeff;
  --accent-2: #0d9488;
  --ok: #12805c;
  --ok-soft: #e4f6ee;
  --warn: #a35a06;
  --warn-soft: #fdf1de;
  --bad: #c8334a;
  --bad-soft: #fdeaed;
  --info: #1f6feb;
  --info-soft: #e9f1fe;
  --violet: #7a3fd6;
  --mark: #fff2b8;
  --code-bg: #0f1420;
  --code-ink: #dfe6f3;
  --code-line: #232b3d;
  --grid: rgba(60, 80, 130, .07);
  --hero-a: rgba(63, 81, 255, .16);
  --hero-b: rgba(13, 148, 136, .14);
  /* figure palette */
  --fig-line: #2b3550;
  --fig-ink: #2b3550;
  --fig-fill: #ffffff;
  --fig-fill-2: #eef1f8;
  --fig-mute: #94a0bd;
  --fig-blue: #2563eb;
  --fig-red: #d1384f;
  --fig-red-soft: #fbe0e4;
  --fig-green: #0f8a5f;
  --fig-green-soft: #dff3ea;
  --fig-amber: #c67f00;
  --fig-amber-soft: #fbeccd;
  --fig-purple: #7c3aed;
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #0a0d14;
  --bg-2: #0d1119;
  --panel: #111725;
  --panel-2: #151d2d;
  --panel-3: #1b2437;
  --line: #202a3e;
  --line-2: #2b3752;
  --ink: #e8edf8;
  --ink-2: #a9b6d1;
  --ink-3: #7c8aad;
  --accent: #7c93ff;
  --accent-ink: #0b1020;
  --accent-soft: #1b2550;
  --accent-2: #2fd4b6;
  --ok: #45d69f;
  --ok-soft: #10301f;
  --warn: #ffc061;
  --warn-soft: #33240c;
  --bad: #ff7d90;
  --bad-soft: #351320;
  --info: #6faefc;
  --info-soft: #10233c;
  --violet: #b79bff;
  --mark: #4d4318;
  --code-bg: #080c15;
  --code-ink: #d8e1f3;
  --code-line: #172033;
  --grid: rgba(140, 170, 255, .07);
  --hero-a: rgba(124, 147, 255, .22);
  --hero-b: rgba(47, 212, 182, .13);
  --shadow-2: 0 18px 40px -20px rgba(0, 0, 0, .8);
  --shadow-3: 0 40px 80px -30px rgba(0, 0, 0, .85);
  --fig-line: #c7d3ee;
  --fig-ink: #dbe4f7;
  --fig-fill: #131b2b;
  --fig-fill-2: #1b2437;
  --fig-mute: #5c6c8f;
  --fig-blue: #7ca6ff;
  --fig-red: #ff8598;
  --fig-red-soft: #3a1622;
  --fig-green: #4ed3a1;
  --fig-green-soft: #10301f;
  --fig-amber: #f5c469;
  --fig-amber-soft: #33240c;
  --fig-purple: #b79bff;
  color-scheme: dark;
}

/* ---------- 2. base ---------- */
*,
*::before,
*::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; scroll-padding-top: 86px; }
body {
  margin: 0;
  font: 400 var(--fs)/var(--lh) var(--font-ui);
  background: var(--bg);
  color: var(--ink);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  font-variant-ligatures: common-ligatures contextual;
  overflow-x: hidden;
}
body::before {
  /* faint dot-grid wash behind everything */
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(1100px 620px at 88% -10%, var(--hero-a), transparent 60%),
    radial-gradient(900px 500px at -5% 8%, var(--hero-b), transparent 60%),
    radial-gradient(var(--grid) 1px, transparent 1px) 0 0/22px 22px;
  pointer-events: none;
}
img, svg { max-width: 100%; }
a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 2.5px; }
a:hover { text-decoration: none; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 4px; }
::selection { background: color-mix(in oklab, var(--accent) 28%, transparent); }
button { font: inherit; color: inherit; cursor: pointer; }
kbd {
  font: 600 .72em/1 var(--font-mono);
  padding: .3em .42em; border-radius: 5px;
  background: var(--panel-3); border: 1px solid var(--line-2);
  border-bottom-width: 2px; color: var(--ink-2);
}
.skip {
  position: absolute; left: -9999px; top: 0; z-index: 99;
  background: var(--accent); color: var(--accent-ink); padding: .7rem 1rem; border-radius: 0 0 8px 0;
}
.skip:focus { left: 0; }
.dim { color: var(--ink-3); }

/* ---------- 3. top bar ---------- */
.progress { position: fixed; inset: 0 0 auto 0; height: 2px; z-index: 60; background: transparent; }
.progress > i {
  display: block; height: 100%; width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  box-shadow: 0 0 12px color-mix(in oklab, var(--accent) 60%, transparent);
}
.topbar {
  position: sticky; top: 0; z-index: 50;
  display: flex; align-items: center; gap: .6rem;
  padding: .55rem clamp(.7rem, 2vw, 1.1rem);
  background: color-mix(in oklab, var(--bg) 82%, transparent);
  backdrop-filter: saturate(150%) blur(14px);
  border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: .6rem; text-decoration: none; color: var(--ink); min-width: 0; }
.brand-mark { width: 30px; height: 30px; display: grid; place-items: center; color: var(--accent); }
.brand-mark svg { width: 100%; height: 100%; }
.brand-text { display: flex; flex-direction: column; line-height: 1.15; min-width: 0; }
.brand-text strong { font-size: 1.02rem; letter-spacing: .16em; font-weight: 750; }
.brand-text span {
  font-size: .66rem; letter-spacing: .09em; text-transform: uppercase;
  color: var(--ink-3); white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}
.topbar-spacer { flex: 1 1 auto; }
.topnav { display: flex; gap: .2rem; }
.topnav a {
  color: var(--ink-2); text-decoration: none; font-size: .87rem; font-weight: 550;
  padding: .42rem .6rem; border-radius: var(--r-sm);
}
.topnav a:hover { background: var(--panel-2); color: var(--ink); }
.search-cta {
  display: flex; align-items: center; gap: .5rem;
  min-width: min(23ch, 30vw);
  padding: .4rem .55rem;
  border: 1px solid var(--line); border-radius: 10px;
  background: var(--panel); color: var(--ink-3); font-size: .84rem;
  box-shadow: var(--shadow-1);
  transition: border-color var(--dur), color var(--dur), transform var(--dur);
}
.search-cta:hover { border-color: var(--accent); color: var(--ink-2); transform: translateY(-1px); }
.search-cta svg { width: 15px; height: 15px; flex: none; opacity: .8; }
.search-cta span { flex: 1 1 auto; text-align: left; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.icon-btn {
  display: grid; place-items: center; width: 34px; height: 34px;
  border: 1px solid transparent; border-radius: 9px; background: transparent; color: var(--ink-2);
  transition: background var(--dur), color var(--dur), border-color var(--dur);
}
.icon-btn:hover { background: var(--panel-2); color: var(--ink); border-color: var(--line); }
.icon-btn svg { width: 19px; height: 19px; }
.i-moon { display: none; }
:root[data-theme="dark"] .i-sun { display: none; }
:root[data-theme="dark"] .i-moon { display: block; }
.only-narrow { display: none; }

/* options popover */
.popover {
  position: fixed; top: 62px; right: max(.9rem, 2vw); z-index: 70;
  width: min(310px, calc(100vw - 1.5rem));
  background: var(--panel); border: 1px solid var(--line); border-radius: var(--r);
  box-shadow: var(--shadow-3); padding: .85rem .95rem 1rem;
  animation: pop var(--dur) var(--ease);
}
@keyframes pop { from { opacity: 0; transform: translateY(-6px) scale(.98); } }
.pop-h { margin: .1rem 0 .4rem; font-size: .7rem; letter-spacing: .1em; text-transform: uppercase; color: var(--ink-3); font-weight: 700; }
.pop-h + .pop-h, .popover .seg + .pop-h { margin-top: .9rem; }
.seg { display: flex; gap: .25rem; background: var(--panel-2); border: 1px solid var(--line); padding: .2rem; border-radius: 10px; }
.seg button {
  flex: 1 1 0; border: 0; background: transparent; color: var(--ink-2);
  padding: .34rem .5rem; border-radius: 7px; font-size: .82rem; font-weight: 550;
  transition: background var(--dur), color var(--dur);
}
.seg button:hover { color: var(--ink); }
.seg button[aria-selected="true"] { background: var(--panel); color: var(--ink); box-shadow: var(--shadow-1); }
.seg.scroll { overflow-x: auto; }
.seg.scroll button { flex: none; }
.switch { display: flex; align-items: center; gap: .5rem; font-size: .86rem; color: var(--ink-2); }
.switch input { accent-color: var(--accent); width: 16px; height: 16px; }

/* ---------- 4. shell ---------- */
.shell {
  display: grid;
  grid-template-columns: 302px minmax(0, 1fr) 252px;
  gap: clamp(1rem, 2.4vw, 2.2rem);
  align-items: start;
  max-width: 1680px;
  margin: 0 auto;
  padding: 0 clamp(.8rem, 2.2vw, 2rem) 3rem;
}
:root[data-width] .main { --pad: 0; }

/* sidebar */
.sidebar {
  position: sticky; top: 57px; max-height: calc(100vh - 57px);
  display: flex; flex-direction: column;
  padding: 1rem 0 0;
  border-right: 1px solid var(--line);
  overscroll-behavior: contain;
}
.side-head { padding: 0 .8rem .7rem 0; }
.side-kicker {
  margin: 0 0 .5rem; font-size: .68rem; font-weight: 750; letter-spacing: .16em;
  text-transform: uppercase; color: var(--ink-3);
}
.side-filter {
  width: 100%; padding: .44rem .6rem; font-size: .85rem;
  border: 1px solid var(--line); border-radius: 9px; background: var(--panel); color: var(--ink);
}
.side-filter::placeholder { color: var(--ink-3); }
.side-filter:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.tree { flex: 1 1 auto; overflow-y: auto; padding: 0 .7rem 2rem 0; scrollbar-width: thin; }
.tree::-webkit-scrollbar { width: 9px; }
.tree::-webkit-scrollbar-thumb { background: var(--line-2); border-radius: 8px; border: 3px solid var(--bg); }
.tree-home {
  display: flex; align-items: center; gap: .5rem; margin-bottom: .7rem;
  font-weight: 650; font-size: .9rem; color: var(--ink-2); text-decoration: none;
  padding: .35rem .45rem; border-radius: 8px;
}
.tree-home:hover { background: var(--panel-2); color: var(--ink); }
.tree-home .mark { color: var(--accent); }
.tnode { margin-bottom: .12rem; }
.tnode > summary {
  display: flex; align-items: center; gap: .5rem; cursor: pointer;
  padding: .38rem .45rem; border-radius: 8px; list-style: none;
  font-weight: 640; font-size: .9rem; letter-spacing: -.005em; color: var(--ink);
}
.tnode > summary::-webkit-details-marker { display: none; }
.tnode > summary::before {
  content: ""; width: 8px; height: 8px; flex: none; margin-left: 1px;
  border-right: 1.7px solid var(--ink-3); border-bottom: 1.7px solid var(--ink-3);
  transform: rotate(-45deg); transition: transform var(--dur) var(--ease);
}
.tnode[open] > summary::before { transform: rotate(45deg); }
.tnode > summary:hover { background: var(--panel-2); }
.tnum {
  font: 700 .68rem/1 var(--font-mono); color: var(--accent);
  background: var(--accent-soft); padding: .28rem .34rem; border-radius: 5px; min-width: 1.5em; text-align: center;
}
.ttitle { flex: 1 1 auto; }
.tcount {
  font: 500 .68rem/1 var(--font-mono); color: var(--ink-3);
  background: var(--panel-2); border-radius: 20px; padding: .22rem .42rem;
}
.tnode ul { margin: .1rem 0 .5rem; padding: 0 0 0 .75rem; list-style: none; border-left: 1px solid var(--line); }
.tleaf {
  display: flex; align-items: baseline; gap: .45rem;
  padding: .28rem .5rem; margin-left: -.55rem;
  border-radius: 7px; font-size: .855rem; color: var(--ink-2); text-decoration: none;
  line-height: 1.4;
}
.tleaf .dot { width: 4px; height: 4px; border-radius: 50%; background: var(--line-2); flex: none; transform: translateY(-2px); }
.tleaf:hover { background: var(--panel-2); color: var(--ink); }
.tleaf.here {
  background: linear-gradient(90deg, var(--accent-soft), transparent);
  color: var(--ink); font-weight: 620; box-shadow: inset 2px 0 0 var(--accent);
}
.tleaf.here .dot { background: var(--accent); width: 5px; height: 5px; }
.tleaf.intro { font-style: italic; color: var(--ink-3); font-size: .82rem; }
.side-foot {
  display: flex; gap: .9rem; padding: .7rem .8rem .9rem 0; margin-top: auto;
  border-top: 1px solid var(--line); font-size: .8rem;
}
.side-foot a { color: var(--ink-3); text-decoration: none; }
.side-foot a:hover { color: var(--accent); }
.scrim {
  position: fixed; inset: 0; z-index: 44; background: rgba(4, 8, 18, .55);
  backdrop-filter: blur(2px);
}

/* right rail */
.rail { position: sticky; top: 76px; max-height: calc(100vh - 90px); overflow: auto; padding: 2.2rem 0 2rem 0; }
.rail-h {
  margin: 0 0 .5rem; font-size: .68rem; font-weight: 750; letter-spacing: .14em;
  text-transform: uppercase; color: var(--ink-3);
}
.rail-list { margin: 0; padding: 0 0 0 .75rem; list-style: none; border-left: 1px solid var(--line); }
.rail-list li { margin: 0; }
.rail-list a {
  display: block; padding: .2rem 0; font-size: .81rem; line-height: 1.42;
  color: var(--ink-3); text-decoration: none; transition: color var(--dur);
}
.rail-list a:hover { color: var(--ink); }
.rail-list li.lvl3 { padding-left: .6rem; font-size: .78rem; }
.rail-list li.active > a { color: var(--accent); font-weight: 600; }
.rail-top { border: 0; background: transparent; color: var(--ink-3); font-size: .78rem; padding: .6rem 0 0; }
.rail-top:hover { color: var(--accent); }

/* ---------- 5. article ---------- */
.main { min-width: 0; }
.page { min-width: 0; }
.page-head, .chap-head { padding-top: 2.1rem; }
.eyebrow {
  margin: 0 0 .55rem; font-size: .73rem; font-weight: 700; letter-spacing: .13em;
  text-transform: uppercase; color: var(--accent);
}
.page-title, .chap-title {
  margin: 0 0 .55rem; font-family: var(--font-display);
  font-size: clamp(1.95rem, 1.25rem + 2.4vw, 2.85rem); line-height: 1.08;
  letter-spacing: -.028em; font-weight: 760; text-wrap: balance;
}
.chap-title { font-size: clamp(2.1rem, 1.4rem + 3vw, 3.4rem); }
.lead {
  margin: .7rem 0 1rem; font-size: 1.12rem; line-height: 1.62; color: var(--ink-2);
  max-width: 68ch; text-wrap: pretty;
}
.lead strong { color: var(--ink); }
.meta-row { display: flex; flex-wrap: wrap; gap: .34rem; margin: 0 0 1.3rem; padding: 0; list-style: none; }
.chip {
  display: inline-flex; align-items: center; gap: .3rem;
  font-size: .735rem; font-weight: 600; letter-spacing: .01em;
  padding: .22rem .5rem; border-radius: 20px;
  background: var(--panel); border: 1px solid var(--line); color: var(--ink-2);
}
.chip.diff-easy { border-color: color-mix(in oklab, var(--ok) 45%, var(--line)); color: var(--ok); background: var(--ok-soft); }
.chip.diff-core { border-color: color-mix(in oklab, var(--accent) 40%, var(--line)); color: var(--accent); background: var(--accent-soft); }
.chip.diff-hard { border-color: color-mix(in oklab, var(--warn) 45%, var(--line)); color: var(--warn); background: var(--warn-soft); }
.chip.diff-olympiad { border-color: color-mix(in oklab, var(--bad) 45%, var(--line)); color: var(--bad); background: var(--bad-soft); }
.chip.cplx { font-family: var(--font-mono); font-size: .72rem; }
.chip.read { color: var(--ink-3); }
.chip.live { color: var(--violet); border-color: color-mix(in oklab, var(--violet) 40%, var(--line)); }
.chip.tag { color: var(--ink-3); }

.prereq {
  float: right; width: min(268px, 42%); margin: .3rem 0 1rem 1.6rem;
  padding: .75rem .85rem; border: 1px solid var(--line); border-radius: var(--r);
  background: var(--panel); box-shadow: var(--shadow-1); font-size: .85rem;
}
.prereq-h { margin: 0 0 .4rem; font-size: .68rem; letter-spacing: .13em; text-transform: uppercase; color: var(--ink-3); font-weight: 700; }
.prereq ul { margin: 0; padding-left: 1.05rem; }
.prereq li { margin: .1rem 0; }
.prereq a { color: var(--ink); text-decoration: none; border-bottom: 1px dashed var(--line-2); }
.prereq a:hover { color: var(--accent); border-color: var(--accent); }
.prereq .miss { color: var(--ink-3); }

.page-body { max-width: var(--maxw); }
:root[data-width="full"] .page-body { max-width: none; }
.page-body > :first-child { margin-top: 0; }
.page-body p, .page-body ul, .page-body ol { max-width: 74ch; }
.page-body h2 {
  margin: 2.6rem 0 .7rem; font-size: 1.5rem; line-height: 1.22; letter-spacing: -.019em;
  font-weight: 700; scroll-margin-top: 90px;
}
.page-body h3 { margin: 1.9rem 0 .5rem; font-size: 1.16rem; letter-spacing: -.011em; font-weight: 660; scroll-margin-top: 90px; }
.page-body h4 { margin: 1.4rem 0 .4rem; font-size: .95rem; letter-spacing: .02em; font-weight: 700; color: var(--ink-2); scroll-margin-top: 90px; }
.page-body h2 + p, .page-body h3 + p { margin-top: 0; }
.page-body p { margin: 0 0 1rem; }
.page-body ul, .page-body ol { margin: 0 0 1.05rem; padding-left: 1.35rem; }
.page-body li { margin: .28rem 0; padding-left: .15rem; }
.page-body li::marker { color: var(--ink-3); }
.page-body li > ul, .page-body li > ol { margin: .3rem 0 .1rem; }
.page-body hr { border: 0; border-top: 1px solid var(--line); margin: 2.2rem 0; }
.page-body blockquote {
  margin: 1.2rem 0; padding: .1rem 0 .1rem 1.05rem; border-left: 3px solid var(--line-2);
  color: var(--ink-2); font-family: var(--font-serif); font-size: 1.02rem;
}
.page-body :not(pre) > code {
  font: 500 .855em/1.45 var(--font-mono);
  background: var(--panel-2); border: 1px solid var(--line); border-radius: 5px;
  padding: .1em .32em; color: color-mix(in oklab, var(--ink) 84%, var(--accent));
  word-break: break-word;
}
.m { font-family: var(--font-serif); font-style: italic; letter-spacing: .01em; white-space: nowrap; }
.m sub, .m sup { font-size: .72em; font-style: normal; }
.m code, .page-body .m :not(pre) > code { background: none; border: 0; padding: 0; }
h2 .m, h3 .m, h1 .m { font-style: normal; font-family: inherit; }
.disp-math {
  margin: 1.3rem 0; padding: .9rem 1rem; text-align: center;
  background: var(--panel); border: 1px solid var(--line); border-radius: var(--r);
  font-size: 1.06rem; overflow-x: auto;
}
.eq-block {
  display: grid; grid-template-columns: 1fr auto; align-items: center; gap: 1rem;
  margin: 1.3rem 0; padding: .85rem 1rem .85rem 1.15rem;
  background: var(--panel); border: 1px solid var(--line); border-left: 3px solid var(--accent);
  border-radius: var(--r); font-size: 1.02rem; font-family: var(--font-serif); font-style: italic;
}
.eqno { font: 500 .8rem/1 var(--font-mono); color: var(--ink-3); font-style: normal; }
.xref { border-bottom: 1px dashed color-mix(in oklab, var(--accent) 55%, transparent); text-decoration: none; font-weight: 560; }
.xref:hover { border-bottom-style: solid; }
.xref-missing { color: var(--ink-3); font: 500 .86em/1 var(--font-mono); background: var(--panel-2); border-radius: 4px; padding: .1em .3em; }
h2[id] .hdr, h3[id] .hdr {
  margin-left: .4rem; opacity: 0; font-weight: 400; text-decoration: none; color: var(--accent);
  transition: opacity var(--dur);
}
h2:hover .hdr, h3:hover .hdr { opacity: .8; }

/* ---------- 6. callouts ---------- */
.callout {
  position: relative; margin: 1.4rem 0; padding: .95rem 1.05rem 1rem;
  border: 1px solid var(--line); border-left: 3px solid var(--ink-3);
  border-radius: var(--r); background: var(--panel); box-shadow: var(--shadow-1);
  max-width: 82ch;
}
.callout > :last-child { margin-bottom: 0; }
.callout > :first-child { margin-top: 0; }
.callout p { max-width: 78ch; }
.cal-head { margin: 0 0 .45rem !important; display: flex; align-items: center; gap: .5rem; flex-wrap: wrap; }
.cal-label {
  font: 700 .665rem/1 var(--font-ui); letter-spacing: .12em; text-transform: uppercase;
  padding: .32rem .48rem; border-radius: 5px;
  background: var(--panel-3); color: var(--ink-2);
}
.cal-title { font-weight: 700; font-size: .98rem; letter-spacing: -.01em; color: var(--ink); }
.cal-info { border-left-color: var(--info); }
.cal-info .cal-label { background: var(--info-soft); color: var(--info); }
.cal-defn { border-left-color: var(--accent); background: linear-gradient(180deg, var(--accent-soft), var(--panel) 70%); }
.cal-defn .cal-label { background: var(--accent); color: var(--accent-ink); }
.cal-thm { border-left-color: var(--violet); }
.cal-thm .cal-label { background: color-mix(in oklab, var(--violet) 16%, transparent); color: var(--violet); }
.cal-thm { background: linear-gradient(180deg, color-mix(in oklab, var(--violet) 8%, var(--panel)), var(--panel) 65%); }
.cal-ok { border-left-color: var(--ok); background: linear-gradient(180deg, var(--ok-soft), var(--panel) 72%); }
.cal-ok .cal-label { background: color-mix(in oklab, var(--ok) 18%, transparent); color: var(--ok); }
.cal-warn { border-left-color: var(--bad); background: linear-gradient(180deg, var(--bad-soft), var(--panel) 72%); }
.cal-warn .cal-label { background: color-mix(in oklab, var(--bad) 18%, transparent); color: var(--bad); }
.cal-accent { border-left-color: var(--accent-2); background: linear-gradient(180deg, color-mix(in oklab, var(--accent-2) 12%, var(--panel)), var(--panel) 70%); }
.cal-accent .cal-label { background: color-mix(in oklab, var(--accent-2) 20%, transparent); color: var(--accent-2); }
.cal-ex { border-left-color: var(--warn); }
.cal-ex .cal-label { background: var(--warn-soft); color: var(--warn); }
.cal-proof { border: 1px dashed var(--line-2); border-left: 3px solid var(--ink-3); background: transparent; box-shadow: none; font-size: .96rem; }
.cal-proof .cal-label { background: var(--panel-3); }
.cal-proof > p:last-child::after { content: " ∎"; color: var(--ink-3); font-weight: 700; }
.cal-muted { background: var(--panel-2); }
.cal-head + p { margin-top: 0; }
.props { margin: 1.3rem 0; padding: .8rem 1rem 1rem; border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); max-width: 78ch; }
.props h4 { margin: 0 0 .45rem; font-size: .72rem; letter-spacing: .13em; text-transform: uppercase; color: var(--ink-3); }
.props ul { margin: 0; padding-left: 1.1rem; }
.props li { margin: .22rem 0; font-size: .95rem; }
ol.steps { list-style: none; margin: 1.3rem 0; padding: 0; counter-reset: s; max-width: 78ch; }
ol.steps li {
  display: grid; grid-template-columns: auto 1fr; gap: .7rem; align-items: start;
  margin: .5rem 0; padding: .55rem .7rem; background: var(--panel);
  border: 1px solid var(--line); border-radius: var(--r-sm);
}
.stepno {
  display: grid; place-items: center; width: 1.5rem; height: 1.5rem; flex: none;
  border-radius: 50%; background: var(--accent); color: var(--accent-ink);
  font: 700 .78rem/1 var(--font-mono);
}
details.fold {
  margin: 1.1rem 0; border: 1px solid var(--line); border-radius: var(--r);
  background: var(--panel); overflow: clip; max-width: 82ch;
}
details.fold > summary {
  cursor: pointer; padding: .6rem .85rem; font-weight: 650; font-size: .92rem;
  list-style: none; display: flex; align-items: center; gap: .5rem;
}
details.fold > summary::-webkit-details-marker { display: none; }
details.fold > summary::before { content: "▸"; color: var(--accent); transition: transform var(--dur); }
details.fold[open] > summary::before { transform: rotate(90deg); }
details.fold > summary:hover { background: var(--panel-2); }
.fold-body { padding: .2rem .9rem 1rem; border-top: 1px solid var(--line); }
.tabs { margin: 1.4rem 0; max-width: 84ch; }
.tab {
  border: 1px solid var(--line); border-bottom: 0; background: var(--panel-2);
  padding: .42rem .8rem; border-radius: 9px 9px 0 0; font-size: .84rem; font-weight: 600;
  color: var(--ink-2);
}
.tab[aria-selected="true"] { background: var(--panel); color: var(--ink); }
.tabpanel { padding: .9rem 1rem 1rem; border: 1px solid var(--line); border-radius: 0 var(--r) var(--r) var(--r); background: var(--panel); }
.grid { display: grid; gap: .8rem; margin: 1.2rem 0; }
.grid.cols-2 { grid-template-columns: repeat(auto-fit, minmax(min(260px, 100%), 1fr)); }
.grid.cols-3 { grid-template-columns: repeat(auto-fit, minmax(min(200px, 100%), 1fr)); }
.cell { padding: .8rem .9rem; border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); }
.cell p:last-child { margin-bottom: 0; }
.chips { display: flex; flex-wrap: wrap; gap: .3rem; margin: .6rem 0; }

/* ---------- 7. code ---------- */
figure.code {
  margin: 1.4rem 0; border-radius: var(--r); overflow: hidden;
  background: var(--code-bg); border: 1px solid var(--code-line);
  box-shadow: var(--shadow-2); max-width: 100%;
  --maxw: none;
}
figure.code figcaption {
  display: flex; align-items: center; gap: .55rem;
  padding: .38rem .5rem .38rem .8rem;
  background: color-mix(in oklab, var(--code-bg) 78%, #6b7fff 22%);
  border-bottom: 1px solid var(--code-line); color: #b9c6e4; font-size: .76rem;
}
figure.code .lang {
  font: 700 .64rem/1 var(--font-mono); letter-spacing: .1em; text-transform: uppercase;
  padding: .26rem .4rem; border-radius: 4px; background: rgba(255, 255, 255, .1); color: #d7e2ff;
}
figure.code .code-title { flex: 1 1 auto; font-family: var(--font-mono); font-size: .78rem; opacity: .9; }
figure.code figcaption .code-title { flex: none; }
.copy {
  margin-left: auto; display: inline-flex; align-items: center; gap: .35rem;
  border: 1px solid rgba(255, 255, 255, .16); background: rgba(255, 255, 255, .05);
  color: #cbd7f0; border-radius: 7px; padding: .28rem .5rem; font-size: .74rem; font-weight: 600;
  transition: background var(--dur), color var(--dur);
}
.copy:hover { background: rgba(255, 255, 255, .14); color: #fff; }
.copy.done { border-color: #45d69f; color: #8ff0c9; }
.code-body { display: flex; overflow: auto; scrollbar-width: thin; }
.code-body::-webkit-scrollbar { height: 9px; }
.code-body::-webkit-scrollbar-thumb { background: #2b3550; border-radius: 8px; }
figure.code pre {
  margin: 0; padding: .85rem .95rem; flex: 1 1 auto; color: var(--code-ink);
  font: 450 .845rem/1.62 var(--font-mono); tab-size: 4; white-space: pre;
  font-variant-ligatures: none;
}
.gutter {
  display: flex; flex-direction: column; padding: .85rem 0; text-align: right;
  user-select: none; border-right: 1px solid var(--code-line); background: rgba(255, 255, 255, .02);
}
.gutter span { padding: 0 .6rem; font: 400 .74rem/1.62 var(--font-mono); color: #55627e; }
.t-k { color: #ffb86c; }
.t-s { color: #9ce09c; }
.t-c { color: #647195; font-style: italic; }
.t-n { color: #d2a8ff; }
.t-f { color: #82aaff; }
.t-y { color: #7fdbca; }
.t-o { color: #89ddff; }
.t-v { color: #f78c6c; }
pre code { background: none; border: 0; padding: 0; color: inherit; }

/* ---------- 8. tables ---------- */
.table-wrap { margin: 1.4rem 0; overflow-x: auto; border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); box-shadow: var(--shadow-1); }
table { border-collapse: collapse; width: 100%; font-size: .92rem; }
thead th {
  text-align: left; padding: .6rem .8rem; font-size: .72rem; letter-spacing: .09em;
  text-transform: uppercase; color: var(--ink-3); background: var(--panel-2);
  border-bottom: 1px solid var(--line); white-space: nowrap; font-weight: 700;
}
tbody td { padding: .58rem .8rem; border-bottom: 1px solid var(--line); vertical-align: top; }
tbody tr:last-child td { border-bottom: 0; }
tbody tr:hover { background: var(--panel-2); }
td code, th code { font-size: .84em; }
td:first-child { font-weight: 600; }

/* ---------- 9. figures ---------- */
figure.fig {
  margin: 1.7rem 0; padding: .9rem; border: 1px solid var(--line); border-radius: var(--r-lg);
  background: var(--panel); box-shadow: var(--shadow-1); text-align: center;
  max-width: 100%;
}
:root[data-grid="off"] figure.fig .gv-box { background-image: none; }
figure.fig .gv-box {
  display: block; margin: 0 auto; width: var(--fig-w, min(100%, 460px)); aspect-ratio: auto;
  padding: .5rem; border-radius: 8px;
  background-color: color-mix(in oklab, var(--panel) 86%, var(--bg));
  background-image: linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 18px 18px;
}
figure.fig .gv-box svg { width: 100%; height: auto; display: block; }
.gv { width: 100%; height: auto; display: block; }
.gv text { fill: var(--fig-ink); font-weight: 500; }
.gv .edge path { stroke-width: 1.25; }
.gv .edge polygon { fill: var(--fig-line); stroke: none; }
figure.fig img { border-radius: 8px; background: var(--panel); }
figcaption { margin-top: .6rem; display: flex; gap: .5rem; justify-content: center; align-items: baseline; flex-wrap: wrap; }
.fignum {
  font: 700 .66rem/1 var(--font-mono); letter-spacing: .1em; text-transform: uppercase;
  color: var(--accent); background: var(--accent-soft); padding: .26rem .42rem; border-radius: 5px;
}
.figcap { font-size: .85rem; color: var(--ink-2); max-width: 60ch; text-align: left; }

/* ---------- 10. demos ---------- */
.demo {
  margin: 1.6rem 0; border: 1px solid var(--line-2); border-radius: var(--r-lg);
  background: linear-gradient(180deg, var(--panel-2), var(--panel) 22%);
  box-shadow: var(--shadow-2); overflow: clip;
}
.demo-shell { display: grid; grid-template-columns: minmax(0, 1fr) 268px; }
.demo-stage { position: relative; min-height: 300px; padding: .5rem; background:
  radial-gradient(var(--grid) 1px, transparent 1px) 0 0/20px 20px; }
.demo-stage svg { display: block; width: 100%; height: 100%; }
.demo-side { border-left: 1px solid var(--line); padding: .7rem .8rem .9rem; display: flex; flex-direction: column; gap: .55rem; min-width: 0; }
.demo-h { font: 700 .68rem/1 var(--font-ui); letter-spacing: .12em; text-transform: uppercase; color: var(--ink-3); margin: .1rem 0 0; }
.demo-bar {
  display: flex; flex-wrap: wrap; align-items: center; gap: .4rem;
  padding: .5rem .7rem; border-bottom: 1px solid var(--line);
  background: color-mix(in oklab, var(--panel) 60%, var(--bg));
}
.demo-title { font-weight: 700; font-size: .92rem; letter-spacing: -.01em; }
.demo-title small { color: var(--ink-3); font-weight: 500; margin-left: .4rem; }
.demo-actions { margin-left: auto; display: flex; gap: .35rem; align-items: center; flex-wrap: wrap; }
.btn {
  display: inline-flex; align-items: center; gap: .35rem;
  padding: .38rem .72rem; border-radius: 9px; font-size: .84rem; font-weight: 620;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink);
  text-decoration: none; box-shadow: var(--shadow-1);
  transition: transform var(--dur) var(--ease), background var(--dur), border-color var(--dur);
}
.btn:hover { transform: translateY(-1px); border-color: var(--line-2); }
.btn:active { transform: translateY(0); }
.btn.primary { background: var(--accent); border-color: transparent; color: var(--accent-ink); }
.btn.primary:hover { background: color-mix(in oklab, var(--accent) 88%, #fff); }
.btn.ghost { background: transparent; box-shadow: none; }
.btn.sm { padding: .22rem .5rem; font-size: .78rem; }
.btn[disabled] { opacity: .45; cursor: not-allowed; transform: none; }
.demo-note { margin: 0; font-size: .8rem; color: var(--ink-2); line-height: 1.5; }
.demo-readout { display: grid; grid-template-columns: auto 1fr; gap: .18rem .6rem; font: 500 .8rem/1.5 var(--font-mono); margin: 0; }
.demo-readout dt { color: var(--ink-3); }
.demo-readout dd { margin: 0; }
.demo-arr { display: flex; flex-wrap: wrap; gap: .22rem; }
.demo-arr .cell {
  padding: .18rem .34rem; border-radius: 5px; font: 600 .78rem/1.3 var(--font-mono);
  background: var(--panel-2); border: 1px solid var(--line); color: var(--ink-2); min-width: 2rem; text-align: center;
}
.demo-arr .cell.on { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.demo-arr .cell.done { background: var(--accent-soft); color: var(--accent); border-color: color-mix(in oklab, var(--accent) 35%, var(--line)); }
.demo-arr .cell.lo { background: var(--bad-soft); color: var(--bad); border-color: color-mix(in oklab, var(--bad) 35%, var(--line)); }
.demo-arr .cell.hi { background: var(--ok-soft); color: var(--ok); border-color: color-mix(in oklab, var(--ok) 35%, var(--line)); }
table.demo-table { font-size: .8rem; width: 100%; }
table.demo-table th, table.demo-table td { padding: .26rem .35rem; border-bottom: 1px solid var(--line); text-align: center; font-family: var(--font-mono); }
table.demo-table th { font-size: .68rem; letter-spacing: .04em; text-transform: none; background: transparent; border-bottom: 1px solid var(--line-2); }
table.demo-table tr.cur td { background: var(--accent-soft); color: var(--ink); font-weight: 700; }
table.demo-table td.inf { color: var(--ink-3); }
table.demo-table td.improved { color: var(--ok); font-weight: 700; }
.demo-log {
  margin: 0; padding: .45rem .6rem; max-height: 132px; overflow: auto;
  font: 500 .77rem/1.5 var(--font-mono); background: var(--code-bg); color: var(--code-ink);
  border-radius: 8px; white-space: pre-wrap;
}
.demo-log .ok { color: #9ce09c; }
.demo-log .bad { color: #ff9aa8; }
.demo-log .mut { color: #647195; }
.demo svg .vtx circle { transition: r var(--dur) var(--ease), fill var(--dur); cursor: pointer; }
.demo svg .vtx text { pointer-events: none; font-weight: 700; }
.demo svg .edg line, .demo svg .edg path { transition: stroke var(--dur), stroke-width var(--dur), opacity var(--dur); }
.demo svg .lbl { font: 500 11px var(--font-mono); fill: var(--ink-2); }
.demo svg .wt {
  font: 700 11px var(--font-mono); fill: var(--ink-2);
  paint-order: stroke; stroke: var(--panel); stroke-width: 3px; stroke-linejoin: round;
}
.demo-cap { margin: -.4rem 0 1.4rem; font-size: .82rem; color: var(--ink-3); max-width: 74ch; }
.demo-loading { padding: 2rem; text-align: center; color: var(--ink-3); font-size: .85rem; }
.gnode.sel circle { stroke: var(--accent); stroke-width: 3; }
.badge-live {
  display: inline-flex; align-items: center; gap: .3rem; font-size: .7rem; font-weight: 700;
  color: var(--violet); background: color-mix(in oklab, var(--violet) 12%, transparent);
  padding: .2rem .4rem; border-radius: 5px; letter-spacing: .06em; text-transform: uppercase;
}

/* ---------- 11. problems ---------- */
section.probset { margin: 2rem 0; }
.probset-h {
  margin: 0 0 .6rem; font-size: .78rem; letter-spacing: .13em; text-transform: uppercase;
  color: var(--ink-3); font-weight: 750;
}
.prob-tabs { display: flex; gap: .3rem; align-items: center; margin: 0 0 .55rem; font-size: .76rem; color: var(--ink-3); flex-wrap: wrap; }
.pfilter {
  border: 1px solid var(--line); background: var(--panel); border-radius: 20px;
  padding: .18rem .55rem; font-size: .76rem; font-weight: 600; color: var(--ink-2);
}
.pfilter[aria-selected="true"] { background: var(--ink); color: var(--bg); border-color: var(--ink); }
.probs { display: grid; gap: .5rem; grid-template-columns: repeat(auto-fill, minmax(min(330px, 100%), 1fr)); }
.probs.wide { margin-bottom: 1.6rem; }
a.prob {
  display: grid; grid-template-columns: auto 1fr; gap: .1rem .6rem; align-items: baseline;
  padding: .6rem .75rem; border: 1px solid var(--line); border-radius: var(--r);
  background: var(--panel); text-decoration: none; color: var(--ink);
  box-shadow: var(--shadow-1); transition: transform var(--dur) var(--ease), border-color var(--dur), box-shadow var(--dur);
}
a.prob:hover { transform: translateY(-2px); border-color: color-mix(in oklab, var(--accent) 45%, var(--line)); box-shadow: var(--shadow-2); }
a.prob .pid {
  font: 700 .7rem/1.3 var(--font-mono); color: var(--accent); background: var(--accent-soft);
  padding: .2rem .38rem; border-radius: 5px; grid-row: span 2; align-self: start; white-space: nowrap;
}
a.prob .pt { font-size: .92rem; font-weight: 600; letter-spacing: -.008em; }
a.prob .pmeta { grid-column: 2; display: flex; gap: .35rem; flex-wrap: wrap; margin-top: .1rem; }
.pm { font-size: .7rem; color: var(--ink-3); background: var(--panel-2); border-radius: 4px; padding: .14rem .34rem; }
.pdiff { font: 700 .66rem/1 var(--font-ui); letter-spacing: .06em; text-transform: uppercase; padding: .22rem .38rem; border-radius: 4px; }
.pd-easy { background: var(--ok-soft); color: var(--ok); }
.pd-core { background: var(--info-soft); color: var(--info); }
.pd-hard { background: var(--warn-soft); color: var(--warn); }
.pd-olympiad, .pd-research { background: var(--bad-soft); color: var(--bad); }
a.prob[hidden] { display: none; }
.prob-toolbar {
  display: flex; align-items: center; gap: .5rem; flex-wrap: wrap;
  padding: .6rem .75rem; margin: 1.2rem 0;
  border: 1px solid var(--line); border-radius: var(--r); background: var(--panel);
  font-size: .78rem; color: var(--ink-3); position: sticky; top: 57px; z-index: 20;
}
.prob-toolbar .seg { flex: 1 1 320px; }
.prob-index h2 {
  display: flex; align-items: center; gap: .6rem; margin: 2.2rem 0 .7rem; font-size: 1.16rem;
}
.h-num { font: 700 .72rem/1 var(--font-mono); color: var(--accent); background: var(--accent-soft); padding: .3rem .4rem; border-radius: 5px; }
.h-n { margin-left: auto; font: 500 .74rem/1 var(--font-mono); color: var(--ink-3); }

/* ---------- 12. chapter + home ---------- */
.chap-stats { display: flex; gap: 1.3rem; flex-wrap: wrap; margin: 1.2rem 0 .2rem; padding: .7rem .9rem; border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); }
.chap-stats span { font-size: .8rem; color: var(--ink-3); }
.chap-stats b { font: 700 1.05rem/1 var(--font-mono); color: var(--ink); display: block; margin-bottom: .2rem; }
.chap-notes { margin: 2rem 0 0; }
.pcards { display: grid; gap: .7rem; grid-template-columns: repeat(auto-fill, minmax(min(310px, 100%), 1fr)); margin: 1.6rem 0 0; }
.pcard {
  position: relative; display: flex; flex-direction: column; gap: .3rem;
  padding: .95rem 1rem 1rem; border: 1px solid var(--line); border-radius: var(--r);
  background: var(--panel); text-decoration: none; color: var(--ink); box-shadow: var(--shadow-1);
  overflow: hidden; transition: transform var(--dur) var(--ease), border-color var(--dur), box-shadow var(--dur);
}
.pcard::after {
  content: ""; position: absolute; inset: auto 0 0 0; height: 2px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transform: scaleX(0); transform-origin: left; transition: transform .3s var(--ease);
}
.pcard:hover { transform: translateY(-3px); box-shadow: var(--shadow-2); border-color: var(--line-2); }
.pcard:hover::after { transform: scaleX(1); }
.pcard-t { font-weight: 700; font-size: 1.03rem; letter-spacing: -.015em; line-height: 1.3; }
.pcard-s { font-size: .875rem; color: var(--ink-2); line-height: 1.5; }
.pcard-meta { display: flex; gap: .3rem; flex-wrap: wrap; margin-top: .35rem; }
.pcard-num { display: none; }
.li-k { font: 500 .7rem/1 var(--font-mono); color: var(--ink-3); }

.page-home { padding-top: .4rem; }
.hero {
  position: relative; display: grid; gap: clamp(1rem, 3vw, 2.6rem);
  grid-template-columns: minmax(0, 1.15fr) minmax(0, .85fr); align-items: center;
  padding: clamp(1.4rem, 4vw, 3rem) 0 clamp(1.4rem, 3vw, 2.4rem);
}
.hero-kick {
  display: flex; align-items: center; gap: .5rem; margin: 0 0 1rem;
  font-size: .76rem; font-weight: 650; letter-spacing: .06em; text-transform: uppercase; color: var(--ink-3);
}
.pulse { width: 7px; height: 7px; border-radius: 50%; background: var(--accent-2); box-shadow: 0 0 0 4px color-mix(in oklab, var(--accent-2) 22%, transparent); }
.hero h1 {
  margin: 0 0 .7rem; font-family: var(--font-display);
  font-size: clamp(2.5rem, 1.1rem + 5.6vw, 4.9rem); line-height: .99; letter-spacing: -.037em;
  font-weight: 780;
}
.hero h1 em {
  font-style: normal;
  background: linear-gradient(100deg, var(--accent), var(--accent-2) 75%);
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.hero-lead { margin: 0 0 1.35rem; font-size: clamp(1rem, .95rem + .35vw, 1.14rem); color: var(--ink-2); max-width: 58ch; line-height: 1.62; }
.hero-cta { display: flex; gap: .5rem; flex-wrap: wrap; margin-bottom: 1.5rem; }
.hero-cta .btn { padding: .55rem .95rem; font-size: .92rem; }
.hero-stats { display: flex; flex-wrap: wrap; gap: .1rem 1.6rem; margin: 0; padding: 1rem 0 0; border-top: 1px solid var(--line); }
.hero-stats div { min-width: 4.6rem; }
.hero-stats dt { font: 700 1.5rem/1 var(--font-mono); letter-spacing: -.03em; color: var(--ink); }
.hero-stats dd { margin: .2rem 0 0; font-size: .74rem; color: var(--ink-3); letter-spacing: .04em; text-transform: uppercase; }
.hero-art { min-width: 0; filter: drop-shadow(0 24px 40px color-mix(in oklab, var(--accent) 22%, transparent)); }
.why {
  display: grid; gap: .8rem; grid-template-columns: repeat(auto-fit, minmax(min(240px, 100%), 1fr));
  margin: 1.4rem 0 2.6rem;
}
.why-item { padding: 1rem 1.05rem; border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); box-shadow: var(--shadow-1); }
.why-item h3 { margin: 0 0 .3rem; font-size: .98rem; letter-spacing: -.01em; }
.why-item p { margin: 0; font-size: .875rem; color: var(--ink-2); line-height: 1.55; }
.htrack { margin: 2.2rem 0 0; }
.htrack h2 {
  display: flex; align-items: baseline; gap: .7rem; margin: 0 0 .9rem;
  font-size: 1.05rem; letter-spacing: .1em; text-transform: uppercase; color: var(--ink-3); font-weight: 750;
}
.htrack h2::after { content: ""; flex: 1 1 auto; height: 1px; background: var(--line); }
.hcards { display: grid; gap: .7rem; grid-template-columns: repeat(auto-fill, minmax(min(272px, 100%), 1fr)); }
.hc {
  position: relative; display: flex; flex-direction: column; gap: .25rem; min-height: 132px;
  padding: .9rem 1rem; border: 1px solid var(--line); border-radius: var(--r-lg);
  background: var(--panel); text-decoration: none; color: var(--ink); overflow: hidden;
  transition: transform var(--dur) var(--ease), box-shadow var(--dur), border-color var(--dur);
}
.hc::before {
  content: ""; position: absolute; inset: 0;
  background: radial-gradient(360px 140px at 90% -20%, var(--accent-soft), transparent 70%);
  opacity: 0; transition: opacity var(--dur);
}
.hc:hover { transform: translateY(-3px); box-shadow: var(--shadow-2); border-color: color-mix(in oklab, var(--accent) 35%, var(--line)); }
.hc:hover::before { opacity: 1; }
.hc-num { font: 700 .74rem/1 var(--font-mono); color: var(--accent); letter-spacing: .06em; }
.hc-t { font-size: 1.12rem; font-weight: 720; letter-spacing: -.02em; line-height: 1.2; }
.hc-s { font-size: .855rem; color: var(--ink-2); line-height: 1.5; flex: 1 1 auto; }
.hc-m { font: 500 .74rem/1 var(--font-mono); color: var(--ink-3); }
.hc-m b { color: var(--ink-2); }
.teasers { display: grid; gap: .5rem; grid-template-columns: repeat(auto-fill, minmax(min(210px, 100%), 1fr)); }
.demo-teaser {
  display: flex; flex-direction: column; gap: .2rem; padding: .7rem .8rem;
  border: 1px solid var(--line); border-radius: var(--r); background: var(--panel);
  text-decoration: none; color: var(--ink); font-size: .87rem; font-weight: 600;
  transition: border-color var(--dur), transform var(--dur);
}
.demo-teaser:hover { border-color: var(--violet); transform: translateY(-2px); }
.demo-teaser .dt-d { font: 500 .72rem/1.4 var(--font-mono); color: var(--violet); text-transform: uppercase; letter-spacing: .06em; }

/* complexity sheet */
.sheet { display: grid; gap: 1rem; grid-template-columns: repeat(auto-fit, minmax(min(400px, 100%), 1fr)); }
.sheet-g { border: 1px solid var(--line); border-radius: var(--r); background: var(--panel); overflow: clip; }
.sheet-g h3 {
  margin: 0; padding: .55rem .8rem; font-size: .74rem; letter-spacing: .13em; text-transform: uppercase;
  color: var(--ink); background: var(--panel-2); border-bottom: 1px solid var(--line);
}
.sheet-g table { font-size: .85rem; }
.sheet-g th:first-child, .t-name { width: 40%; }
.t-time { white-space: nowrap; }
.sheet-note { font-size: .84rem; color: var(--ink-2); margin-top: 1.2rem; }

/* ---------- 13. page footer ---------- */
.pn-row { display: grid; grid-template-columns: 1fr 1fr; gap: .7rem; margin: 3.2rem 0 0; }
.pn {
  display: flex; flex-direction: column; gap: .15rem; padding: .85rem 1rem;
  border: 1px solid var(--line); border-radius: var(--r); background: var(--panel);
  text-decoration: none; color: var(--ink); transition: border-color var(--dur), transform var(--dur);
}
.pn:hover { border-color: var(--accent); transform: translateY(-2px); }
.pn.next { text-align: right; }
.pn.empty { border: 0; background: transparent; }
.pn-k { font-size: .7rem; letter-spacing: .12em; text-transform: uppercase; color: var(--ink-3); font-weight: 700; }
.pn-t { font-weight: 700; letter-spacing: -.015em; font-size: 1.02rem; }
.pn-c { font-size: .78rem; color: var(--ink-3); }
.page-foot {
  display: flex; gap: 1rem; flex-wrap: wrap; align-items: center; justify-content: space-between;
  margin: 1.1rem 0 0; padding: .9rem 0 3rem; border-top: 1px solid var(--line);
  font-size: .8rem; color: var(--ink-3);
}
.pf-left { display: flex; gap: .9rem; align-items: center; flex-wrap: wrap; }
.pf-h { color: var(--ink-3); }
.page-foot a { color: var(--ink-2); text-decoration: none; border-bottom: 1px dashed var(--line-2); }
.page-foot a:hover { color: var(--accent); border-color: var(--accent); }

/* ---------- 14. search palette ---------- */
.palette {
  position: fixed; inset: 0; z-index: 90; display: grid; place-items: start center;
  padding: 9vh 1rem 1rem; background: rgba(6, 10, 20, .55); backdrop-filter: blur(6px);
  animation: fade .16s var(--ease);
}
@keyframes fade { from { opacity: 0; } }
.palette[hidden] { display: none; }
.palette-box {
  width: min(720px, 100%); max-height: 78vh; display: flex; flex-direction: column;
  background: var(--panel); border: 1px solid var(--line-2); border-radius: var(--r-lg);
  box-shadow: var(--shadow-3); overflow: hidden; animation: rise .2s var(--ease);
}
@keyframes rise { from { transform: translateY(10px) scale(.99); opacity: 0; } }
.palette-input { display: flex; align-items: center; gap: .6rem; padding: .8rem .9rem; border-bottom: 1px solid var(--line); }
.palette-input svg { width: 17px; height: 17px; color: var(--ink-3); flex: none; }
.palette-input input { flex: 1 1 auto; border: 0; background: transparent; font: 500 1.02rem/1.3 var(--font-ui); color: var(--ink); }
.palette-input input:focus { outline: none; }
.palette-hits { overflow-y: auto; padding: .4rem; }
.hit {
  display: block; padding: .55rem .7rem; border-radius: 9px; text-decoration: none; color: var(--ink);
  border: 1px solid transparent;
}
.hit:hover, .hit.sel { background: var(--panel-2); border-color: var(--line); }
.hit-t { font-weight: 660; font-size: .95rem; letter-spacing: -.01em; }
.hit-c { font-size: .7rem; color: var(--accent); text-transform: uppercase; letter-spacing: .1em; font-weight: 700; margin-right: .4rem; }
.hit-s { font-size: .82rem; color: var(--ink-2); line-height: 1.45; margin-top: .15rem; }
.hit mark { background: var(--mark); color: inherit; border-radius: 3px; padding: 0 .1em; }
.hit-an { font: 500 .74rem/1.4 var(--font-mono); color: var(--ink-3); margin-top: .2rem; }
.palette-foot {
  display: flex; gap: 1rem; padding: .5rem .9rem; border-top: 1px solid var(--line);
  font-size: .72rem; color: var(--ink-3); background: var(--panel-2);
}
.palette-empty { padding: 1.4rem; text-align: center; color: var(--ink-3); font-size: .88rem; }

/* ---------- 15. responsive ---------- */
@media (max-width: 1400px) {
  .shell { grid-template-columns: 284px minmax(0, 1fr); }
  .rail { display: none; }
}
@media (max-width: 1080px) {
  .hero { grid-template-columns: 1fr; }
  .hero-art { order: -1; max-width: 340px; }
}
@media (max-width: 900px) {
  .shell { grid-template-columns: minmax(0, 1fr); }
  .only-narrow { display: grid; }
  .sidebar {
    position: fixed; inset: 57px auto 0 0; width: min(320px, 86vw); z-index: 45;
    background: var(--panel); border-right: 1px solid var(--line);
    padding: .8rem .2rem 0 1rem; transform: translateX(-102%);
    transition: transform .26s var(--ease); box-shadow: var(--shadow-3);
  }
  body.nav-open .sidebar { transform: none; }
  .prereq { float: none; width: auto; margin: 1.2rem 0; }
  .search-cta span { display: none; }
  .search-cta { min-width: 0; }
  .topnav { display: none; }
  .demo-shell { grid-template-columns: 1fr; }
  .demo-side { border-left: 0; border-top: 1px solid var(--line); }
}
@media (max-width: 620px) {
  .page-body { font-size: .98rem; }
  .pn-row { grid-template-columns: 1fr; }
  .probs { grid-template-columns: 1fr; }
  .hero-stats { gap: .6rem 1rem; }
  figure.fig .gv-box { width: 100%; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .001ms !important; transition-duration: .001ms !important; }
  html { scroll-behavior: auto; }
}

/* ---------- 16. print ---------- */
@media print {
  :root { --bg: #fff; --panel: #fff; --ink: #000; --ink-2: #222; --line: #ccc; }
  .topbar, .sidebar, .rail, .progress, .pn-row, .demo .demo-bar, .copy, .page-foot, .palette { display: none !important; }
  .shell { display: block; padding: 0; }
  .page-body h2 { break-after: avoid; }
  figure.code, figure.fig, .callout, .demo, a.prob, .pcard { break-inside: avoid; box-shadow: none; }
  a[href^="http"]::after { content: " (" attr(href) ")"; font-size: .75em; color: #555; }
  body::before { display: none; }
}