/* One left-aligned reading column, hairline structure, a single live figure on the home page. */
:root{
  --bg:#f6f7f5;--fg:#121614;--muted:#5d645f;--faint:#626b65;--line:#dfe3df;--soft:#eceeeb;--card:#fbfcfb;
  --accent:#157a48;--brand:#2ec46d;--fill:rgba(46,196,109,.16);
  --sans:"IBM Plex Sans",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --mono:"IBM Plex Mono",ui-monospace,SFMono-Regular,Menlo,monospace;
  --col:720px;
}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){--bg:#0f1211;--fg:#e6eae7;--muted:#9aa29c;--faint:#8d958f;--line:#232927;--soft:#171c1a;--card:#131715;--accent:#52d48c;--fill:rgba(46,196,109,.14);color-scheme:dark}}
:root[data-theme="dark"]{--bg:#0f1211;--fg:#e6eae7;--muted:#9aa29c;--faint:#8d958f;--line:#232927;--soft:#171c1a;--card:#131715;--accent:#52d48c;--fill:rgba(46,196,109,.14);color-scheme:dark}

*{box-sizing:border-box}
html{background:var(--bg);-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--fg);font:16.5px/1.65 var(--sans);-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility}
.skip{position:absolute;left:12px;top:-60px;z-index:20;background:var(--fg);color:var(--bg);padding:8px 12px;border-radius:6px;text-decoration:none;font:500 .85rem var(--mono)}
.skip:focus{top:10px}
::selection{background:var(--brand);color:#0b0f0d}
:focus-visible{outline:2px solid var(--accent);outline-offset:3px;border-radius:3px}
.wrap{max-width:var(--col);margin:0 auto;padding-left:max(20px,env(safe-area-inset-left,0px));padding-right:max(20px,env(safe-area-inset-right,0px))}

/* header */
header{position:sticky;top:0;z-index:10;background:color-mix(in srgb,var(--bg) 86%,transparent);backdrop-filter:blur(10px);-webkit-backdrop-filter:blur(10px);border-bottom:1px solid var(--line)}
nav{max-width:var(--col);margin:0 auto;padding:14px max(20px,env(safe-area-inset-right,0px)) 14px max(20px,env(safe-area-inset-left,0px));display:flex;flex-wrap:wrap;gap:4px 20px;align-items:center}
nav .brand{font-family:var(--sans);font-size:.98rem;display:inline-flex;align-items:center;gap:9px;font-weight:600;letter-spacing:-.01em;margin-right:auto;color:var(--fg);text-decoration:none}
.mark{width:20px;height:20px;flex:none}
.mark .s{fill:currentColor}
.mark .g{fill:var(--brand)}
nav a{color:var(--muted);text-decoration:none;font:500 .8rem/1 var(--mono);letter-spacing:.02em;padding:6px 0;transition:color .15s}
nav a:hover{color:var(--fg)}
nav a[aria-current="page"]:not(.brand){color:var(--fg)}
nav a[aria-current="page"]:not(.brand)::before{content:"";display:inline-block;width:6px;height:6px;margin-right:7px;border-radius:1px;background:var(--brand);transform:translateY(-1px) rotate(18deg)}

/* type */
main{max-width:var(--col);margin:0 auto;padding:72px max(20px,env(safe-area-inset-right,0px)) 88px max(20px,env(safe-area-inset-left,0px))}
.eyebrow{font:500 .74rem/1.4 var(--mono);letter-spacing:.1em;text-transform:uppercase;color:var(--faint);margin:0 0 18px}
.eyebrow b{color:var(--accent);font-weight:500}
h1{font-size:clamp(2.1rem,6vw,3.1rem);line-height:1.06;letter-spacing:-.035em;font-weight:500;margin:0 0 .5em;text-wrap:balance}
h2{font:500 .74rem/1.4 var(--mono);letter-spacing:.1em;text-transform:uppercase;color:var(--faint);margin:52px 0 14px;padding-top:16px;border-top:1px solid var(--line)}
h3{font-size:1.05rem;font-weight:600;letter-spacing:-.01em;margin:1.6em 0 .3em}
p{margin:.7em 0;max-width:62ch;overflow-wrap:break-word}
dd,li{overflow-wrap:break-word}
.lead{font-size:1.16rem;line-height:1.55;color:var(--muted);max-width:36em;text-wrap:pretty}
a{color:var(--accent);text-underline-offset:3px;text-decoration-thickness:1px}
a:hover{text-decoration-thickness:2px}
code{font:.86em var(--mono);background:var(--soft);border-radius:4px;padding:.12em .36em}
ul,ol{padding-left:1.2em}
li{margin:.4em 0}
main ul{list-style:none;padding-left:0}
main ul li{position:relative;padding-left:22px;max-width:62ch}
main ul li::before{content:"";position:absolute;left:2px;top:.66em;width:6px;height:6px;border-radius:1px;background:var(--brand);transform:rotate(18deg)}

/* buttons */
.actions{display:flex;flex-wrap:wrap;gap:10px;margin:28px 0 8px}
.btn{display:inline-flex;align-items:center;gap:8px;padding:10px 16px;border-radius:6px;font-weight:500;font-size:.94rem;text-decoration:none;border:1px solid var(--line);color:var(--fg);background:transparent;transition:border-color .15s,background .15s}
.btn:hover{border-color:var(--muted)}
.btn.primary{background:var(--fg);color:var(--bg);border-color:var(--fg)}
.btn.primary:hover{opacity:.88}

/* hero figure: a random simplicial complex with its Betti numbers */
.complex{margin:48px 0 0;border:1px solid var(--line);border-radius:8px;background:var(--card);overflow:hidden}
.complex canvas{display:block;width:100%;height:230px}
.complex figcaption{display:flex;flex-wrap:wrap;gap:6px 18px;align-items:center;padding:11px 14px;border-top:1px solid var(--line);font:.78rem/1.4 var(--mono);color:var(--muted);font-variant-numeric:tabular-nums}
.complex figcaption .betti{color:var(--fg)}
.complex figcaption .betti b{color:var(--accent);font-weight:500}
.complex button{margin-left:auto;font:inherit;color:var(--muted);background:none;border:1px solid var(--line);border-radius:4px;padding:4px 9px;cursor:pointer}
.complex button:hover{color:var(--fg);border-color:var(--muted)}

/* definition rows (families) */
.rows{display:grid;margin:0}
.rows>div{display:grid;grid-template-columns:13rem 1fr;gap:4px 24px;padding:14px 0;border-bottom:1px solid var(--line)}
.rows>div:first-child{border-top:1px solid var(--line)}
.rows dt{font-weight:600;letter-spacing:-.005em}
.rows dd{margin:0;color:var(--muted);min-width:0}
@media (max-width:620px){.rows>div{grid-template-columns:1fr}}

/* numbered steps (a real sequence) */
ol.steps{list-style:none;padding:0;margin:0;counter-reset:s;display:grid;gap:0}
ol.steps li{counter-increment:s;position:relative;padding:14px 0 14px 44px;margin:0;border-bottom:1px solid var(--line);max-width:none}
ol.steps li:first-child{border-top:1px solid var(--line)}
ol.steps li::before{content:counter(s);position:absolute;left:0;top:14px;font:500 .8rem/1.65 var(--mono);color:var(--accent)}

.note{border-left:2px solid var(--brand);padding:.2em 0 .2em 14px;color:var(--muted)}
.tablewrap{overflow-x:auto;margin:16px 0;border:1px solid var(--line);border-radius:8px}
table{border-collapse:collapse;width:100%;min-width:560px;font-size:.9rem}
th,td{border-bottom:1px solid var(--line);padding:10px 12px;text-align:left}
tbody tr:last-child td{border-bottom:0}
th{background:var(--soft);font:500 .72rem/1.4 var(--mono);letter-spacing:.06em;text-transform:uppercase;color:var(--muted)}
td.p{color:var(--muted);font:italic .82rem var(--mono)}
pre{background:var(--card);border:1px solid var(--line);border-radius:8px;padding:16px;overflow-x:auto;font:.83rem/1.7 var(--mono);margin:16px 0}
pre code{background:none;padding:0;font-size:1em}
pre .c{color:var(--faint)}
pre .k{color:var(--accent)}

/* closing call to action */
.cta{margin-top:72px;padding:28px;border:1px solid var(--line);border-radius:8px;background:var(--card)}
.cta h2{margin:0 0 8px;padding:0;border:0}
.cta p{margin:.3em 0}
.cta .actions{margin:18px 0 0}

footer{max-width:var(--col);margin:0 auto;padding:22px max(20px,env(safe-area-inset-right,0px)) 48px max(20px,env(safe-area-inset-left,0px));border-top:1px solid var(--line);color:var(--faint);font-size:.84rem;display:flex;gap:10px;align-items:flex-start}
footer .mark{width:16px;height:16px;margin-top:3px;color:var(--faint)}
footer a{color:var(--muted)}
@media (max-width:560px){nav{gap:2px 16px;padding-top:10px;padding-bottom:8px}nav .brand{flex-basis:100%;margin-bottom:4px}main{padding-top:44px}h2{margin-top:56px}}
@media (prefers-reduced-motion:reduce){*{transition:none!important}}