:root {
  --bg: #03050b;
  --ink: #e9edf5;
  --ink-2: #aeb8c9;
  --ink-3: #6f7a8e;
  --glass: rgba(12, 16, 28, 0.62);
  --glass-edge: rgba(160, 185, 230, 0.14);
  --accent: #ffd58a;
  --accent-2: #9cc6ff;
  --serif: 'Newsreader', 'Iowan Old Style', 'Palatino Linotype', Palatino, Georgia, serif;
  --sans: 'Inter', ui-sans-serif, system-ui, -apple-system, 'Segoe UI', sans-serif;
  --mono: ui-monospace, 'SF Mono', Menlo, monospace;
  --gutter: max(16px, env(safe-area-inset-left));
  color-scheme: dark;
}
* { box-sizing: border-box; }
/* Elements with their own display (flex, grid) must still honor the hidden attribute. */
[hidden] { display: none !important; }
html, body { margin: 0; height: 100%; background: var(--bg); color: var(--ink); font: 15px/1.5 var(--sans); overflow: hidden; -webkit-font-smoothing: antialiased; }
#scene { position: fixed; inset: 0; width: 100vw; height: 100vh; height: 100dvh; display: block; touch-action: none; outline: none; cursor: grab; background: radial-gradient(120% 90% at 50% 40%, #0a1022 0%, #050811 55%, #020308 100%); }
#scene.dragging { cursor: grabbing; }
#scene.hovering { cursor: pointer; }
#veil { position: fixed; inset: 0; background: #000; opacity: 0; pointer-events: none; transition: opacity 0.35s ease; z-index: 30; }
#veil.on { opacity: 1; }

button, select, input { font: inherit; color: inherit; }
button { background: rgba(255, 255, 255, 0.06); border: 1px solid rgba(255, 255, 255, 0.10); border-radius: 9px; padding: 6px 11px; cursor: pointer; transition: background 0.15s, border-color 0.15s; white-space: nowrap; }
button:hover { background: rgba(255, 255, 255, 0.12); border-color: rgba(255, 255, 255, 0.2); }
button:focus-visible, select:focus-visible, input:focus-visible { outline: 2px solid var(--accent-2); outline-offset: 2px; }
button[aria-pressed="true"] { background: rgba(156, 198, 255, 0.18); border-color: rgba(156, 198, 255, 0.55); color: #fff; }
button.icon { width: 32px; height: 32px; padding: 0; display: inline-grid; place-items: center; font-size: 16px; line-height: 1; }
/* Touch: every button takes taps over at least 44 × 44 px without changing how it looks; packed rows grow only
   vertically, so a tap never lands on a neighbour. */
@media (pointer: coarse) {
  :where(button) { position: relative; }
  button::after { content: ''; position: absolute; inset: min(0px, (100% - 44px) / 2); }
  .seg button::after, #c-dots button::after { left: 0; right: 0; }
}
button.primary { background: rgba(255, 213, 138, 0.16); border-color: rgba(255, 213, 138, 0.5); color: #fff3dc; }
a { color: var(--accent-2); }

.glass { background: var(--glass); border: 1px solid var(--glass-edge); border-radius: 16px; -webkit-backdrop-filter: blur(18px) saturate(140%); backdrop-filter: blur(18px) saturate(140%); box-shadow: 0 10px 40px rgba(0, 0, 0, 0.35); }

/* Brand */
#brand { position: fixed; top: max(14px, env(safe-area-inset-top)); left: var(--gutter); z-index: 5; pointer-events: none; }
#brand h1 { margin: 0; font: 400 30px/1 var(--serif); letter-spacing: 0.01em; }
#brand .sub { margin: 4px 0 0; color: var(--ink-2); font: italic 15px/1.2 var(--serif); }

/* Chapter card */
#chapter { position: fixed; left: var(--gutter); bottom: max(16px, env(safe-area-inset-bottom)); width: min(440px, calc(100vw - 2 * var(--gutter))); padding: 16px 18px 12px; z-index: 6; }
.chapter-head { display: flex; justify-content: space-between; align-items: center; }
.eyebrow { font: 600 11px/1 var(--sans); letter-spacing: 0.14em; text-transform: uppercase; color: var(--accent); }
#chapter h2 { margin: 6px 0 6px; font: 400 23px/1.2 var(--serif); }
#c-body { font: 16.5px/1.5 var(--serif); color: #dfe5ef; }
#c-body p { margin: 0 0 8px; }
#c-body .math, .math { font-family: var(--serif); font-style: italic; white-space: nowrap; }
#c-body .do { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0 2px; font-family: var(--sans); }
#c-body .do button { font-size: 13.5px; }
.chapter-nav { display: flex; align-items: center; justify-content: space-between; gap: 8px; margin-top: 8px; }
#c-dots { display: flex; gap: 6px; list-style: none; margin: 0; padding: 0; }
#c-dots button { width: 22px; height: 22px; padding: 0; border-radius: 50%; font-size: 11px; color: var(--ink-3); background: transparent; border-color: rgba(255, 255, 255, 0.12); }
#c-dots button[aria-current="step"] { color: #10131c; background: var(--accent); border-color: var(--accent); }
#chapter.collapsed #c-body, #chapter.collapsed h2 { display: none; }

/* Inspector */
#inspector { position: fixed; top: max(14px, env(safe-area-inset-top)); right: var(--gutter); width: 300px; padding: 14px 16px; z-index: 6; }
#inspector .kind { margin: 0; font: 600 11px/1 var(--sans); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-3); }
#inspector .kind .swatch { display: inline-block; width: 8px; height: 8px; border-radius: 50%; margin-right: 6px; vertical-align: 0; }
#inspector .poly { margin: 8px 0 8px; font: 400 27px/1.15 var(--serif); overflow-wrap: anywhere; }
#inspector dl { display: grid; grid-template-columns: auto 1fr; gap: 3px 12px; margin: 0; font-size: 13.5px; }
#inspector dt { color: var(--ink-3); }
#inspector dd { margin: 0; font-family: var(--serif); font-size: 16px; text-align: right; overflow-wrap: anywhere; }
#inspector .note { margin: 10px 0 0; color: var(--ink-2); font: italic 14.5px/1.4 var(--serif); }
#inspector .note:empty { display: none; }
#inspector .actions { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 10px; }
#inspector .actions:empty { display: none; }
#inspector .actions button { font-size: 13px; }
#inspector.preview { opacity: 0.86; }

/* Dock */
#dock { position: fixed; right: var(--gutter); bottom: max(16px, env(safe-area-inset-bottom)); display: flex; align-items: center; gap: 10px; padding: 8px 10px; z-index: 7; flex-wrap: wrap; justify-content: flex-end; max-width: calc(100vw - 2 * var(--gutter)); }
.seg { display: inline-flex; gap: 3px; }
.more { display: contents; }
#dock-toggle { display: none; }
#inspector .compact { display: none; }
.seg button { padding: 6px 10px; }
.morph { display: inline-flex; flex-direction: column; gap: 2px; width: 230px; }
.morph-labels { display: flex; justify-content: space-between; font: 500 10.5px/1 var(--sans); color: var(--ink-3); letter-spacing: 0.04em; }
input[type="range"] { -webkit-appearance: none; appearance: none; width: 100%; height: 18px; background: transparent; }
input[type="range"]::-webkit-slider-runnable-track { height: 3px; border-radius: 2px; background: linear-gradient(90deg, rgba(255,255,255,0.12), rgba(156,198,255,0.5)); }
input[type="range"]::-moz-range-track { height: 3px; border-radius: 2px; background: rgba(156,198,255,0.4); }
input[type="range"]::-webkit-slider-thumb { -webkit-appearance: none; width: 16px; height: 16px; margin-top: -6.5px; border-radius: 50%; background: #fff; box-shadow: 0 0 0 3px rgba(156,198,255,0.35); }
input[type="range"]::-moz-range-thumb { width: 16px; height: 16px; border: 0; border-radius: 50%; background: #fff; }
button.xr { background: rgba(255, 213, 138, 0.14); border-color: rgba(255, 213, 138, 0.45); }

.readout { position: fixed; top: max(18px, env(safe-area-inset-top)); left: 50%; transform: translateX(-50%); font: 15px/1 var(--serif); font-style: italic; color: var(--ink-2); z-index: 5; pointer-events: none; transition: opacity 0.3s; }
.readout:empty { opacity: 0; }

/* Sheets */
.sheet { position: fixed; right: var(--gutter); bottom: 86px; width: min(380px, calc(100vw - 2 * var(--gutter))); max-height: calc(100dvh - 120px); overflow: auto; padding: 16px 18px; z-index: 9; }
.sheet h3 { margin: 4px 0 10px; font: 400 21px/1.2 var(--serif); }
.sheet label { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin: 8px 0; font-size: 14px; color: var(--ink-2); }
.sheet label.check { justify-content: flex-start; }
.sheet select { background: rgba(255,255,255,0.06); border: 1px solid rgba(255,255,255,0.12); border-radius: 8px; padding: 4px 8px; }
.sheet input[type="range"] { width: 160px; }
.sheet p { font: 15px/1.5 var(--serif); color: #d8deea; }
.sheet .fine { font: 13px/1.4 var(--sans); color: var(--ink-3); }
.sheet > button { margin-top: 8px; }
.keys-list { padding-left: 18px; margin: 0 0 6px; font-size: 14px; color: var(--ink-2); }
.keys-list li { margin: 4px 0; }
#s-legend { margin: 4px 0 10px; font-size: 12px; color: var(--ink-3); }
#s-bar { height: 8px; border-radius: 4px; }
#s-legend .ticks { display: flex; justify-content: space-between; margin-top: 2px; }
#s-legend .keys { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 6px; }
#s-legend i { display: inline-block; width: 8px; height: 8px; border-radius: 50%; margin-right: 5px; }

/* Inside: the HUD and the Flatland retina */
#inside-hud { position: fixed; top: calc(max(14px, env(safe-area-inset-top)) + 64px); left: var(--gutter); width: min(400px, calc(100vw - 2 * var(--gutter))); padding: 10px 14px; z-index: 6; }
#inside-hud .eye { display: flex; align-items: center; gap: 10px; font-size: 13px; color: var(--ink-2); }
#inside-hud .eye input { flex: 1; }
#inside-hud .eye span { width: 74px; text-align: right; font: italic 14px var(--serif); color: var(--ink); }
#inside-hud dl { display: grid; grid-template-columns: auto 1fr; gap: 2px 12px; margin: 6px 0 4px; font-size: 13px; }
#inside-hud dt { color: var(--ink-3); }
#inside-hud dd { margin: 0; font: 15px var(--serif); text-align: right; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
#inside-hud .turns { font-family: var(--mono); font-size: 12.5px; letter-spacing: 0.06em; color: var(--accent); direction: rtl; }
#inside-hud .hint { margin: 2px 0 6px; font-size: 12px; color: var(--ink-3); }
#inside-hud .row { display: flex; gap: 6px; }
#inside-hud .row button { font-size: 12.5px; padding: 4px 9px; }
#retina { position: fixed; left: 0; right: 0; top: 42%; height: 72px; width: 100vw; z-index: 3; image-rendering: pixelated; border-top: 1px solid rgba(160,190,240,0.25); border-bottom: 1px solid rgba(160,190,240,0.25); background: #02030a; }
#retina-caption { position: fixed; left: 50%; top: calc(42% + 80px); transform: translateX(-50%); width: min(560px, 90vw); text-align: center; font: italic 15px/1.4 var(--serif); color: var(--ink-2); z-index: 3; margin: 0; }

/* The roots pane, side by side with the lattice */
#roots-overlay { position: fixed; pointer-events: none; z-index: 2; display: none; }
body.split #roots-overlay, body.roots-only #roots-overlay { display: block; }
body.split::after { content: ''; position: fixed; top: 0; bottom: 0; right: var(--pane-w); width: 1px; background: rgba(160, 185, 230, 0.16); z-index: 2; pointer-events: none; }
#roots-head { position: fixed; top: max(14px, env(safe-area-inset-top)); right: calc(var(--pane-w) / 2); transform: translateX(50%); display: flex; align-items: center; gap: 8px; padding: 6px 8px 6px 14px; z-index: 6; border-radius: 999px; }
#roots-head .t { font: italic 16px var(--serif); color: var(--ink-2); }
#roots-head .seg button, #roots-head > button { padding: 4px 10px; font-size: 13px; border-radius: 999px; }
body.split #dock { right: calc(var(--pane-w) + var(--gutter)); max-width: calc(100vw - var(--pane-w) - 2 * var(--gutter) - 220px); top: max(14px, env(safe-area-inset-top)); bottom: auto; }
body.split #inspector { top: 120px; }
body.split #inspector { right: calc(var(--pane-w) + var(--gutter)); }
body.split #inside-hud { max-width: calc(100vw - var(--pane-w) - 2 * var(--gutter)); top: 124px; }
body.split .readout { top: auto; bottom: max(22px, env(safe-area-inset-bottom)); left: auto; right: calc(var(--pane-w) + var(--gutter)); transform: none; max-width: calc(100vw - var(--pane-w) - 500px); text-align: right; line-height: 1.35; }
body.inside .readout { display: none; }
body.split .sheet { right: calc(var(--pane-w) + var(--gutter)); }
/* With room right of the tour card, the inspector sits low, off the subject framed up and to the right; the readout
   takes its place under the dock. */
@media (min-width: 1400px) {
  body.split #inspector { top: auto; bottom: max(16px, env(safe-area-inset-bottom)); max-height: calc(100dvh - 150px); overflow: auto; }
  body.split .readout { top: 124px; bottom: auto; }
}
body.roots-only #chapter, body.roots-only #inside-hud, body.roots-only #labels { display: none; }

/* Labels on the boundary of the sky */
#labels { position: fixed; inset: 0; pointer-events: none; z-index: 4; }
#labels span { position: absolute; transform: translate(-50%, -50%); font: italic 15px/1 var(--serif); color: rgba(220, 230, 250, 0.72); text-shadow: 0 0 6px #000; white-space: nowrap; }
#labels span.big { font-size: 17px; color: rgba(255, 236, 200, 0.85); }
#labels span.axis { font-size: 16px; color: rgba(190, 205, 235, 0.62); }

#fatal, .fatal { position: fixed; inset: auto 16px 50% 16px; text-align: center; font: 18px/1.5 var(--serif); z-index: 50; }

/* Medium widths: the dock moves to the top so it never covers the tour card. */
@media (min-width: 761px) and (max-width: 1180px) {
  #dock { top: max(14px, env(safe-area-inset-top)); bottom: auto; max-width: calc(100vw - 230px); }
  .morph { width: 180px; }
  #inspector { top: 82px; max-height: calc(100dvh - 96px); overflow: auto; }
  .sheet { bottom: auto; top: 82px; }
}
/* Narrow screens: the tour becomes a bottom sheet, the dock sits above it. */
@media (max-width: 760px) {
  #brand { top: max(10px, env(safe-area-inset-top)); }
  #brand h1 { font-size: 21px; }
  #brand .sub { display: none; }
  #dock { left: auto; right: 10px; top: max(8px, env(safe-area-inset-top)); bottom: auto; gap: 5px; padding: 5px; flex-wrap: nowrap; max-width: calc(100vw - 120px); }
  #dock .seg button { padding: 5px 9px; font-size: 13.5px; }
  .morph { display: none; }
  #dock-toggle { display: inline-grid; }
  #roots-head { top: auto; bottom: max(12px, env(safe-area-inset-bottom)); right: 50%; }
  body.roots-only #roots-head { bottom: auto; top: 56px; }
  #roots-head .t { display: none; }   /* the model buttons say what the pane is; at 360 px the label clipped ⌂ */
  .more { display: none; }
  #dock.open { flex-wrap: wrap; max-width: calc(100vw - 20px); left: 10px; }
  #dock.open .more { display: contents; }
  #dock.open .morph { display: inline-flex; width: 100%; order: 9; }
  #inspector { top: auto; left: 10px; right: 10px; width: auto; bottom: calc(env(safe-area-inset-bottom) + 134px); padding: 9px 12px; }
  #inspector .kind { display: none; }
  #inspector .poly { font-size: 21px; margin: 0; display: inline; }
  #inspector .compact { display: inline; margin-left: 10px; color: var(--ink-2); font: italic 14px/1.3 var(--serif); }
  #inspector:not(.expanded) dl, #inspector:not(.expanded) .note, #inspector:not(.expanded) .actions { display: none; }
  #inspector.expanded .compact { display: none; }
  #inspector.expanded dl { margin-top: 6px; }
  #chapter { left: 10px; right: 10px; width: auto; bottom: max(10px, env(safe-area-inset-bottom)); padding: 10px 14px 8px; max-height: 46dvh; overflow: auto; }
  #chapter h2 { font-size: 19px; margin: 4px 0; }
  #c-body { font-size: 15px; }
  #chapter:not(.expanded) #c-body { display: none; }
  #c-dots { display: none; }
  #dock .seg button { padding: 5px 8px; font-size: 13px; }
  #chapter.expanded ~ #inspector { display: none; }
  .readout { top: auto; bottom: calc(env(safe-area-inset-bottom) + 172px); font-size: 13px; width: 92vw; text-align: center; }
  .sheet { left: 10px; right: 10px; width: auto; bottom: auto; top: 60px; max-height: calc(100dvh - 80px); }
  #inside-hud { top: 56px; left: 10px; right: 10px; width: auto; transform: none; padding: 8px 10px; }
  #inside-hud .hint { display: none; }
}
/* ?clean hides the interface (screenshots, link previews, recordings). */
body.clean #chapter, body.clean #dock, body.clean #inspector, body.clean #roots-head, body.clean #g-readout, body.clean #inside-hud, body.clean #help, body.clean #settings { display: none !important; }
@media (prefers-reduced-motion: reduce) { #veil { transition: none; } }