/* Both panels share surface and grid colors; textured surfaces use lighter lines. */
:root{
  --bg:#FBFAF8; --panel:#FFFFFF; --ink:#1A1A1A; --muted:#6B6560; --rule:#E2DDD6;
  --accent:#7D1922; --accent-soft:rgba(125,25,34,.12);
  --plane:#3F79B8; --plane-soft:rgba(63,121,184,.16);
  --sphere:#D2CBBF; --grat:#332E27; --grid:#2E90CC;
  --grat-tex:#F4E9D2; --grid-tex:#7FC4F5;
}
@media (prefers-color-scheme: dark){
  :root:not([data-ui="light"]){
    --bg:#14130F; --panel:#1D1B17; --ink:#EDE8E0; --muted:#9C948A; --rule:#332F29;
    --accent:#E0616D; --accent-soft:rgba(224,97,109,.18);
    --plane:#89BCEE; --plane-soft:rgba(137,188,238,.20);
    --sphere:#9A9184; --grat:#191410; --grid:#1B3E75;
    --grat-tex:#F4E9D2; --grid-tex:#7FC4F5;
  }
}
:root[data-ui="dark"]{
  --bg:#14130F; --panel:#1D1B17; --ink:#EDE8E0; --muted:#9C948A; --rule:#332F29;
  --accent:#E0616D; --accent-soft:rgba(224,97,109,.18);
  --plane:#89BCEE; --plane-soft:rgba(137,188,238,.20);
  --sphere:#9A9184; --grat:#191410; --grid:#1B3E75;
  --grat-tex:#F4E9D2; --grid-tex:#7FC4F5;
}

*{box-sizing:border-box}
body{margin:0;background:var(--bg);color:var(--ink);
  font-family:'Public Sans',system-ui,-apple-system,sans-serif;
  font-size:16px;line-height:1.6;-webkit-font-smoothing:antialiased}
.wrap{max-width:1180px;margin:0 auto;padding:32px 24px 72px}

.eyebrow{font-size:13px;letter-spacing:.06em;text-transform:uppercase;color:var(--muted);margin-bottom:10px}
a.home{color:inherit;text-decoration:none;border-bottom:1px solid var(--rule)}
a.home:hover{border-bottom-color:var(--accent);color:var(--accent)}
h1{font-family:'Newsreader',Georgia,serif;font-weight:600;font-size:clamp(28px,4.4vw,42px);
  line-height:1.15;margin:0 0 10px;letter-spacing:-.01em}
.standfirst{font-family:'Newsreader',Georgia,serif;font-size:clamp(17px,2.1vw,20px);
  color:var(--muted);margin:0 0 28px;max-width:64ch}

/* ---- the two panels ---------------------------------------------------- */
.figure{display:grid;grid-template-columns:1fr 1fr;gap:18px;align-items:start}
@media (max-width:900px){ .figure{grid-template-columns:1fr} }

.pane{background:var(--panel);border:1px solid var(--rule);border-radius:10px;overflow:hidden;
  display:flex;flex-direction:column}
.pane-head{display:flex;justify-content:space-between;align-items:baseline;gap:12px;
  padding:11px 14px;border-bottom:1px solid var(--rule)}
.pane-title{font-size:13px;font-weight:600;letter-spacing:.03em;text-transform:uppercase}
.pane-note{font-size:12.5px;color:var(--muted);font-family:'IBM Plex Mono',ui-monospace,monospace}
.stage{position:relative;aspect-ratio:1/1;width:100%}
/* The shared canvas overlays both stages; pointer events pass through. */
.figure{position:relative}
#gpu{position:absolute;inset:0;width:100%;height:100%;display:block;pointer-events:none;z-index:1}
#stage3d{cursor:grab;touch-action:none}
#stage3d.dragging{cursor:grabbing}
.hint{position:absolute;left:12px;bottom:10px;font-size:12px;color:var(--muted);
  background:var(--panel);padding:3px 8px;border-radius:5px;border:1px solid var(--rule);
  pointer-events:none;opacity:.92;z-index:2}

/* ---- controls ---------------------------------------------------------- */
.controls{margin-top:18px;background:var(--panel);border:1px solid var(--rule);
  border-radius:10px;padding:16px 18px}
.row{display:flex;flex-wrap:wrap;gap:22px 30px;align-items:center}
.row-2{margin-top:14px}
.ctl{display:flex;align-items:center;gap:10px;font-size:14px}
.ctl label{color:var(--muted);white-space:nowrap}
/* Custom track fill for Safari. --p is the thumb position (0..1);
   the fill ends at its center: 9px + p * (track width - 18px). */
input[type=range]{-webkit-appearance:none;appearance:none;width:190px;height:20px;margin:0;
  background:transparent;cursor:pointer;--p:.32}
input[type=range]::-webkit-slider-runnable-track{height:5px;border-radius:3px;
  background:linear-gradient(to right,var(--accent) 0 calc(9px + (100% - 18px)*var(--p)),#E9E9ED 0)}
input[type=range]::-moz-range-track{height:5px;border-radius:3px;
  background:linear-gradient(to right,var(--accent) 0 calc(9px + (100% - 18px)*var(--p)),#E9E9ED 0)}
input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;appearance:none;box-sizing:border-box;
  width:18px;height:18px;margin-top:-6.5px;border-radius:50%;background:#fff;
  border:1px solid rgba(0,0,0,.25);box-shadow:0 1px 2px rgba(0,0,0,.3)}
input[type=range]::-moz-range-thumb{box-sizing:border-box;width:18px;height:18px;border-radius:50%;
  background:#fff;border:1px solid rgba(0,0,0,.25);box-shadow:0 1px 2px rgba(0,0,0,.3)}
input[type=range]:focus-visible{outline:2px solid var(--accent);outline-offset:3px}
input[type=checkbox]{accent-color:var(--accent);width:15px;height:15px}
.val{font-family:'IBM Plex Mono',ui-monospace,monospace;font-size:13.5px;
  min-width:4.5ch;text-align:right}
.seg{display:inline-flex;border:1px solid var(--rule);border-radius:7px;overflow:hidden}
.seg button{appearance:none;border:0;background:transparent;color:var(--muted);
  font:inherit;font-size:13px;padding:5px 11px;cursor:pointer}
.seg button[aria-pressed=true]{background:var(--accent-soft);color:var(--accent);font-weight:600}
.btn{appearance:none;border:1px solid var(--rule);background:transparent;color:var(--ink);
  font:inherit;font-size:13px;padding:5px 12px;border-radius:7px;cursor:pointer}
.btn:hover{border-color:var(--accent);color:var(--accent)}
.note{font-size:12.5px;color:var(--muted);font-family:'IBM Plex Mono',ui-monospace,monospace}
.note.warn{color:var(--accent)}
.ctl input:disabled + label{opacity:.45}
.ctl input:disabled{opacity:.45}

/* ---- readout ----------------------------------------------------------- */
.readout{margin-top:18px;display:grid;grid-template-columns:repeat(3,1fr);gap:14px}
@media (max-width:700px){ .readout{grid-template-columns:1fr} }
.stat{background:var(--panel);border:1px solid var(--rule);border-radius:10px;padding:14px 16px}
.stat .k{font-size:12px;letter-spacing:.05em;text-transform:uppercase;color:var(--muted)}
.stat .n{font-family:'IBM Plex Mono',ui-monospace,monospace;font-size:21px;margin-top:5px}
.stat .s{font-size:12.5px;color:var(--muted);margin-top:3px}

.prose{margin-top:34px;max-width:68ch}
.prose h2{font-family:'Newsreader',Georgia,serif;font-weight:600;font-size:22px;margin:26px 0 8px}
.prose p{margin:0 0 14px}
.legend{display:flex;flex-wrap:wrap;gap:16px;margin:14px 0 0;font-size:13px;color:var(--muted)}
/* child combinator, never a descendant selector - KaTeX nests spans deeply */
.legend > span{display:inline-flex;align-items:center;gap:7px}
.swatch{width:13px;height:13px;border-radius:3px;display:inline-block}
/* classes, not inline style attributes: the page CSP forbids those */
.sw-accent{background:var(--accent)} .sw-plane{background:var(--plane)} .sw-grid{background:var(--grid)}

footer{margin-top:56px;padding-top:18px;border-top:1px solid var(--rule);
  font-size:13px;color:var(--muted)}