:root {
  --bg: #f6f7fb;
  --panel: #ffffff;
  --panel-2: #f1f3f9;
  --ink: #161a2b;
  --muted: #5d6479;
  --line: #dfe3ee;
  --accent: #2f5bea;
  --accent-ink: #ffffff;
  --accent-soft: #e7edff;
  --ok: #137a43;
  --ok-soft: #e3f5ea;
  --bad: #c0292b;
  --bad-soft: #fde8e8;
  --warn: #9a5b00;
  --warn-soft: #fff3dc;
  --na: #6b7280;
  --na-soft: #eef0f4;
  --c0: #2f5bea;
  --c1: #e2702a;
  --shade: rgba(47, 91, 234, 0.16);
  --band: rgba(19, 122, 67, 0.12);
  --grid: #e6e9f2;
  --shadow: 0 1px 2px rgba(20, 24, 40, 0.06), 0 6px 24px rgba(20, 24, 40, 0.06);
  --radius: 14px;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  color-scheme: light;
}
:root[data-theme="dark"] {
  --bg: #0f1220;
  --panel: #171b2d;
  --panel-2: #1e2338;
  --ink: #e8ebf5;
  --muted: #9aa2bb;
  --line: #2b3150;
  --accent: #7b9bff;
  --accent-ink: #0d1020;
  --accent-soft: #232c52;
  --ok: #4fd18b;
  --ok-soft: #133024;
  --bad: #ff7a7a;
  --bad-soft: #3a1a1f;
  --warn: #ffc261;
  --warn-soft: #3a2c12;
  --na: #a0a7ba;
  --na-soft: #252a3d;
  --c0: #7b9bff;
  --c1: #ffa25e;
  --shade: rgba(123, 155, 255, 0.22);
  --band: rgba(79, 209, 139, 0.14);
  --grid: #262c45;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 30px rgba(0, 0, 0, 0.25);
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.55 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  -webkit-text-size-adjust: 100%;
}
a { color: var(--accent); }
.hidden { display: none !important; }
.muted { color: var(--muted); }
.small { font-size: 0.86rem; }
.none { color: var(--muted); font-style: italic; }

/* Header */
.topbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
  padding: 10px 16px;
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: 8px; min-width: 0; }
.backlink { text-decoration: none; color: var(--muted); font-size: 0.9rem; white-space: nowrap; }
.sep { color: var(--line); }
.appname { white-space: nowrap; }
.logo {
  display: inline-grid; place-items: center; width: 24px; height: 24px; border-radius: 7px;
  background: var(--accent); color: var(--accent-ink); font-size: 0.95rem; margin-right: 2px;
}
.topactions { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; justify-content: flex-end; }
.credits { font-size: 0.88rem; color: var(--muted); white-space: nowrap; }
.topup { font-size: 0.88rem; font-weight: 600; }

button { font: inherit; cursor: pointer; }
button:disabled { cursor: not-allowed; opacity: 0.55; }
.ghost {
  background: transparent; color: var(--ink); border: 1px solid var(--line);
  border-radius: 10px; padding: 6px 12px;
}
.ghost:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.ghost.icon { padding: 6px 10px; }
.ghost.small, .primary.small { padding: 5px 10px; font-size: 0.88rem; }
.primary {
  background: var(--accent); color: var(--accent-ink); border: 0; border-radius: 12px;
  padding: 11px 20px; font-weight: 650;
}
.primary:hover:not(:disabled) { filter: brightness(1.07); }
.linkbtn { background: none; border: 0; color: var(--accent); padding: 0; font-size: 0.9rem; }
.linkbtn:hover { text-decoration: underline; }

main { max-width: 860px; margin: 0 auto; padding: 8px 16px 40px; }

/* Hero */
.hero { padding: 26px 0 6px; }
.hero h1 { font-size: clamp(1.7rem, 4.6vw, 2.4rem); line-height: 1.15; margin: 0 0 10px; letter-spacing: -0.02em; }
.lede { margin: 0 0 10px; font-size: 1.06rem; color: var(--muted); max-width: 680px; }
.pitch { margin: 0; font-size: 0.93rem; color: var(--muted); }
.pill {
  display: inline-block; background: var(--ok-soft); color: var(--ok); font-weight: 650;
  border-radius: 999px; padding: 1px 10px; margin-right: 6px; font-size: 0.85rem;
}

/* Examples */
.examples { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 18px 0 12px; }
.exlabel { font-size: 0.88rem; color: var(--muted); margin-right: 2px; }
.chip {
  background: var(--panel); color: var(--ink); border: 1px solid var(--line); border-radius: 999px;
  padding: 5px 12px; font-size: 0.9rem;
}
.chip:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.chip-warn { border-style: dashed; }

/* Cards */
.card {
  background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 18px; margin: 14px 0;
}
.lbl { display: block; font-weight: 650; margin-bottom: 6px; }
.lbl.small { font-weight: 500; font-size: 0.88rem; color: var(--muted); }
textarea, input[type="search"], select {
  width: 100%; font: inherit; color: var(--ink); background: var(--panel-2);
  border: 1px solid var(--line); border-radius: 10px; padding: 10px 12px;
}
#problem { font-family: var(--mono); font-size: 1rem; resize: vertical; min-height: 96px; }
textarea:focus, input:focus, select:focus { outline: 2px solid var(--accent); outline-offset: 1px; border-color: transparent; }
select { width: auto; padding: 6px 8px; }

.symbar { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 4px; }
.sym {
  min-width: 42px; padding: 5px 9px; border-radius: 8px; border: 1px solid var(--line);
  background: var(--panel-2); color: var(--ink); font-size: 0.92rem;
}
.sym:hover { border-color: var(--accent); color: var(--accent); }

.preview {
  margin-top: 12px; border: 1px dashed var(--line); border-radius: 12px; padding: 10px 12px; background: var(--panel-2);
}
.prevhead { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; font-size: 0.86rem; }
.prevlabel { color: var(--muted); }
.freetag {
  margin-left: auto; font-size: 0.75rem; color: var(--ok); background: var(--ok-soft);
  padding: 1px 8px; border-radius: 999px; font-weight: 600; white-space: nowrap;
}
h3 .freetag { margin-left: 8px; vertical-align: middle; }
.previewtex { overflow-x: auto; padding: 4px 0; }
.previewtex p { margin: 6px 0; }
.preview p.small { margin: 2px 0 0; }
.freenum {
  margin-top: 8px; display: flex; flex-direction: column; gap: 2px; padding: 8px 10px;
  border-radius: 10px; background: var(--accent-soft);
}
.numlabel { font-size: 0.8rem; font-weight: 650; color: var(--accent); }
.numval { font-family: var(--mono); font-size: 0.95rem; word-break: break-word; }

.tag {
  display: inline-block; font-size: 0.78rem; padding: 1px 9px; border-radius: 999px;
  background: var(--accent-soft); color: var(--accent); font-weight: 600;
}
.notice {
  margin-top: 10px; padding: 8px 12px; border-radius: 10px; background: var(--warn-soft); color: var(--warn); font-size: 0.9rem;
}
.runrow { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 12px; margin-top: 14px; }
.lvl { font-size: 0.9rem; color: var(--muted); display: flex; align-items: center; gap: 8px; }
.runbox { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.meter { font-size: 0.84rem; color: var(--muted); }
.gate {
  margin-top: 10px; padding: 8px 12px; border-radius: 10px; background: var(--bad-soft); color: var(--bad); font-size: 0.9rem;
}
.gate p { margin: 0; }
.gate .topup { margin-left: 6px; }
#runNote { margin: 8px 0 0; }

/* Progress */
.progress .proghead { display: flex; justify-content: space-between; align-items: baseline; gap: 10px; }
.elapsed { font-family: var(--mono); color: var(--muted); font-size: 0.9rem; }
.stagelist { list-style: none; margin: 12px 0 0; padding: 0; display: grid; gap: 6px; }
.stage { display: flex; gap: 10px; align-items: center; color: var(--muted); font-size: 0.94rem; }
.stagedot {
  width: 22px; height: 22px; border-radius: 50%; display: inline-grid; place-items: center;
  font-size: 0.74rem; border: 1px solid var(--line); flex: none;
}
.stage.done { color: var(--ink); }
.stage.done .stagedot { background: var(--ok); border-color: var(--ok); color: #fff; }
.stage.now { color: var(--ink); font-weight: 600; }
.stage.now .stagedot { border-color: var(--accent); color: var(--accent); animation: pulse 1.2s ease-in-out infinite; }
@keyframes pulse { 50% { box-shadow: 0 0 0 5px var(--accent-soft); } }
@media (prefers-reduced-motion: reduce) { .stage.now .stagedot { animation: none; } }

/* Result */
.reshead { display: flex; justify-content: space-between; align-items: flex-start; gap: 12px; flex-wrap: wrap; }
.reshead h2 { margin: 0 0 6px; font-size: 1.3rem; line-height: 1.25; }
.tags { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.verdict {
  border: 0; border-radius: 999px; padding: 6px 14px; font-weight: 700; font-size: 0.9rem; white-space: nowrap;
}
.verdict.v-verified { background: var(--ok-soft); color: var(--ok); }
.verdict.v-mismatch { background: var(--bad-soft); color: var(--bad); }
.verdict.v-inconclusive, .verdict.v-unchecked { background: var(--na-soft); color: var(--na); }
.statuszone { margin-top: 12px; padding: 10px 12px; border-radius: 10px; background: var(--warn-soft); color: var(--warn); }
.statuszone p { margin: 0; }
.restated { margin: 14px 0 6px; font-size: 1.05rem; }
.approach { color: var(--muted); margin: 6px 0 0; }
.given h3, .stepshead h3, .checkpanel h3, .plotzone h3, .mistakes h3, .notes h3 { font-size: 1rem; margin: 18px 0 8px; }
.plain { margin: 0; padding-left: 20px; }

.stepshead { display: flex; justify-content: space-between; align-items: center; gap: 10px; flex-wrap: wrap; }
.switch { font-size: 0.88rem; color: var(--muted); display: flex; gap: 6px; align-items: center; cursor: pointer; }
.steps { list-style: none; margin: 0; padding: 0; display: grid; gap: 10px; counter-reset: none; }
.step { border: 1px solid var(--line); border-radius: 12px; padding: 12px 14px; background: var(--panel); }
.stephead { display: flex; gap: 10px; align-items: baseline; }
.stepnum {
  flex: none; width: 26px; height: 26px; border-radius: 8px; display: inline-grid; place-items: center;
  background: var(--accent-soft); color: var(--accent); font-weight: 700; font-size: 0.88rem;
}
.steptitle { font-size: 1rem; }
.stepexp { margin: 6px 0 4px 36px; }
.step .mathblock { margin: 4px 0 4px 36px; }
.steptools { margin: 6px 0 0 36px; }
.mathblock { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.mathinline .katex { font-size: 1.04em; }
.texsrc { font-family: var(--mono); font-size: 0.92em; background: var(--panel-2); padding: 0 4px; border-radius: 4px; }
.revealrow { margin-top: 10px; }

.askbox { margin: 10px 0 0 36px; padding: 10px; border-radius: 10px; background: var(--panel-2); border: 1px solid var(--line); }
.askbox textarea { background: var(--panel); }
.askrow { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; margin-top: 8px; }
.explain {
  margin: 10px 0 0 36px; padding: 10px 12px; border-left: 3px solid var(--accent); background: var(--accent-soft);
  border-radius: 0 10px 10px 0;
}
.explain p { margin: 6px 0; }
.exhead { display: block; }
.exanswer { font-weight: 500; }
.excorr { color: var(--bad); font-weight: 600; }
.exkey { font-weight: 600; }
.exwatch { color: var(--warn); }
.substeps { margin: 6px 0; padding-left: 20px; }

.final {
  margin: 18px 0 4px; padding: 14px 16px; border-radius: 12px; border: 2px solid var(--accent);
  background: var(--accent-soft); transition: filter 0.2s;
}
.final.veiled { filter: blur(7px); user-select: none; }
.finallabel { font-size: 0.8rem; font-weight: 700; color: var(--accent); text-transform: uppercase; letter-spacing: 0.04em; }
.finaltex .katex-display { margin: 6px 0; font-size: 1.15em; }
.finaltext { margin: 2px 0 0; font-weight: 600; }

.checkpanel { margin-top: 10px; padding: 4px 14px 10px; border-radius: 12px; border: 1px solid var(--line); }
.checkpanel.v-verified { border-color: color-mix(in srgb, var(--ok) 45%, var(--line)); }
.checkpanel.v-mismatch { border-color: var(--bad); background: var(--bad-soft); }
.checksummary { margin: 0 0 8px; }
.checklist, .reconlist { list-style: none; padding: 0; margin: 0; display: grid; gap: 6px; }
.checklist li { display: flex; gap: 10px; align-items: flex-start; }
.mark { flex: none; width: 22px; height: 22px; border-radius: 50%; display: inline-grid; place-items: center; font-size: 0.8rem; font-weight: 700; }
.checklist .ok .mark { background: var(--ok); color: #fff; }
.checklist .bad .mark { background: var(--bad); color: #fff; }
.checklist .na .mark { background: var(--na-soft); color: var(--na); }
.cbody { display: flex; flex-direction: column; min-width: 0; }
.cbody strong { font-family: var(--mono); font-size: 0.88rem; font-weight: 600; word-break: break-word; }
.cdetail { font-size: 0.88rem; color: var(--muted); }
.reconlist { margin-top: 8px; }
.recon { font-size: 0.9rem; padding: 6px 10px; border-radius: 8px; }
.recon.warn { background: var(--bad-soft); color: var(--bad); }
.recon.ok { background: var(--ok-soft); color: var(--ok); }
.recon.info { background: var(--na-soft); color: var(--muted); }
#checkNote { margin: 10px 0 0; }

.plotwrap { width: 100%; }
.plot { width: 100%; height: auto; display: block; border-radius: 10px; background: var(--panel-2); }
.plot .grid line { stroke: var(--grid); stroke-width: 1; }
.plot .grid text { fill: var(--muted); font-size: 11px; font-family: var(--mono); }
.plot .axis { stroke: var(--muted); stroke-width: 1.2; }
.plot .curve { fill: none; stroke-width: 2.4; stroke-linejoin: round; }
.plot .curve.c0 { stroke: var(--c0); }
.plot .curve.c1 { stroke: var(--c1); }
.plot .curve.dashed { stroke-dasharray: 7 6; }
.plot .shade { fill: var(--shade); stroke: none; }
.plot .band { fill: var(--band); }
.plot .pt { fill: var(--c1); stroke: var(--panel); stroke-width: 2; }
.plot .pt.hollow { fill: var(--panel); stroke: var(--bad); stroke-width: 2.5; }

.mistakes ul { margin: 0; padding-left: 20px; }
.notes p { margin: 0; color: var(--muted); }
.exports { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 18px; padding-top: 14px; border-top: 1px solid var(--line); }
.raw { white-space: pre-wrap; word-break: break-word; font-family: var(--mono); font-size: 0.85rem; background: var(--panel-2); padding: 10px; border-radius: 10px; }

/* History */
.histhead { display: flex; justify-content: space-between; gap: 12px; align-items: center; flex-wrap: wrap; }
.histhead h2 { margin: 0; font-size: 1.1rem; }
.histhead input { max-width: 280px; }
.histlist { display: grid; gap: 8px; margin: 8px 0 12px; }
.hitem {
  text-align: left; display: flex; flex-direction: column; gap: 2px; width: 100%;
  background: var(--panel-2); color: var(--ink); border: 1px solid var(--line); border-radius: 10px; padding: 9px 12px;
}
.hitem:hover { border-color: var(--accent); }
.htop { display: flex; justify-content: space-between; gap: 10px; align-items: center; }
.hsub { font-family: var(--mono); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.tag.v-verified { background: var(--ok-soft); color: var(--ok); }
.tag.v-mismatch { background: var(--bad-soft); color: var(--bad); }
.tag.v-inconclusive, .tag.v-unchecked { background: var(--na-soft); color: var(--na); }

.how summary { cursor: pointer; font-weight: 650; }
.how ol { padding-left: 20px; }
.how li { margin: 8px 0; }

.foot { max-width: 860px; margin: 0 auto; padding: 10px 16px 40px; color: var(--muted); font-size: 0.9rem; }
.foot p { margin: 4px 0; }

.toasts { position: fixed; bottom: 16px; left: 50%; transform: translateX(-50%); display: grid; gap: 8px; z-index: 50; width: min(92vw, 520px); }
.toast { padding: 10px 14px; border-radius: 10px; box-shadow: var(--shadow); font-size: 0.92rem; transition: opacity 0.5s; }
.toast.ok { background: var(--ok-soft); color: var(--ok); border: 1px solid var(--ok); }
.toast.err { background: var(--bad-soft); color: var(--bad); border: 1px solid var(--bad); }
.toast.gone { opacity: 0; }

@media (max-width: 560px) {
  .backlink, .sep { display: none; }
  .card { padding: 14px; }
  .stepexp, .step .mathblock, .steptools, .askbox, .explain { margin-left: 0; }
  .runbox { width: 100%; }
  .runbox .primary { width: 100%; }
  .histhead input { max-width: none; }
}

@media print {
  .topbar, .examples, #form, .exports, .history, .how, .foot, .toasts, .steptools, .askbox, .switch, .revealrow { display: none !important; }
  body { background: #fff; color: #000; }
  .card { box-shadow: none; border: 0; }
  .final.veiled { filter: none; }
}

/* ---- Docs pages (api.html, tokens.html) --------------------------------- */
main.doc { max-width: 900px; }
main.doc h2 { margin-top: 1.75rem; }
main.doc p { max-width: 72ch; }
main.doc ul { max-width: 72ch; }
main.doc pre { background: var(--panel-2); border: 1px solid var(--line); border-radius: 8px;
  padding: .8rem; overflow-x: auto; font-size: .82rem; line-height: 1.55;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
main.doc pre.block { display: inline-block; padding: .35rem .6rem; }
main.doc code { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: .88em;
  background: var(--panel-2); border-radius: 4px; padding: .05rem .28rem; }
main.doc pre code { background: none; padding: 0; }
.errtable { width: 100%; border-collapse: collapse; margin: .75rem 0 1rem; font-size: .88rem;
  display: block; overflow-x: auto; }
.errtable th, .errtable td { border: 1px solid var(--line); padding: .45rem .6rem;
  text-align: left; vertical-align: top; }
.errtable th { background: var(--panel-2); font-weight: 600; }
.codegroup { margin: .75rem 0 1.25rem; }
.tabs { display: flex; gap: .25rem; flex-wrap: wrap; margin-bottom: .4rem; }
.tab { background: transparent; color: var(--muted); border: 1px solid var(--line);
  border-radius: 6px 6px 0 0; padding: .25rem .6rem; font-size: .8rem; }
.tab.active { color: var(--ink); background: var(--panel-2); border-bottom-color: var(--panel-2); }
.tab:hover { color: var(--ink); }
.statebox { border: 1px solid var(--line); border-radius: 8px; padding: .8rem;
  background: var(--panel-2); margin: .75rem 0 1.25rem; }
.tokenrow { display: flex; gap: .5rem; flex-wrap: wrap; align-items: center; margin: .5rem 0; }
.tokenbox { flex: 1 1 20rem; background: var(--panel-2); border: 1px solid var(--line);
  border-radius: 8px; padding: .55rem .7rem; font-size: .82rem; word-break: break-all;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
.mini { background: transparent; color: var(--ink); padding: .3rem .6rem; font-size: .82rem; }
.mini:hover:enabled { background: var(--panel-2); }
.mono { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
.mini { border: 1px solid var(--line); border-radius: 8px; }
.statebox p { margin: .3rem 0; }

/* Long display math scrolls inside its own box instead of widening the page:
 * grid and flex children default to min-width:auto, which lets a wide KaTeX
 * line push its column (and the page) past the viewport. */
.steps > li, .step, .final, .explain, .checkpanel, .preview, .cbody { min-width: 0; max-width: 100%; }
.mathblock, .finaltex, .previewtex { max-width: 100%; overflow-x: auto; overflow-y: hidden; }
.katex-display { overflow-x: auto; overflow-y: hidden; max-width: 100%; }