/* ------------------------------------------------------------------
   Relativity, Visualized — styles
   Colors are tokens; canvas drawings read the same tokens (see draw.js)
------------------------------------------------------------------- */
:root {
  --bg: #f7f5f0;
  --panel: #ffffff;
  --sidebar: #f1eee7;
  --ink: #1c1c1e;
  --ink2: #5d5d63;
  --ink3: #8d8d93;
  --hair: #e3dfd6;
  --grid: #e9e6de;
  --surface: #ece8df;
  --accent: #2f5bd3;
  --accent-soft: rgba(47, 91, 211, 0.09);

  /* semantic drawing colors */
  --c-light: #d99a0b;   /* light, photons, signals */
  --c-you: #2f5bd3;     /* you / the observer / things at rest */
  --c-mover: #d9482b;   /* the traveler / things in motion */
  --c-third: #1f8f7f;   /* a third party */
  --c-fourth: #7a52c7;  /* a fourth party */
  --c-mass: #8a6a3b;    /* matter, earth, stars */

  --serif: "Newsreader", "Iowan Old Style", "Palatino Linotype", Georgia, serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;

  --radius: 14px;
  --shadow: 0 1px 2px rgba(20, 20, 30, 0.04), 0 8px 24px rgba(20, 20, 30, 0.05);
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #131417;
  --panel: #1b1c20;
  --sidebar: #17181b;
  --ink: #ececef;
  --ink2: #a9a9b1;
  --ink3: #75757e;
  --hair: #2b2c31;
  --grid: #26272c;
  --surface: #2a2c31;
  --accent: #7ea2ff;
  --accent-soft: rgba(126, 162, 255, 0.12);
  --c-light: #f2bf3d;
  --c-you: #7ea2ff;
  --c-mover: #ff7a5c;
  --c-third: #4cc4b0;
  --c-fourth: #b292ff;
  --c-mass: #c9a26a;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px rgba(0, 0, 0, 0.25);
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 3px; }

/* ---------------- layout ---------------- */
.app { display: grid; grid-template-columns: 300px minmax(0, 1fr); min-height: 100vh; }
.sidebar {
  position: sticky; top: 0; height: 100vh; overflow-y: auto;
  background: var(--sidebar); border-right: 1px solid var(--hair);
  padding: 22px 0 40px;
  scrollbar-width: thin;
}
.topbar, .scrim { display: none; }
.main { padding: 40px 56px 80px; max-width: 1080px; width: 100%; outline: none; }

/* ---------------- brand ---------------- */
.brand { display: flex; align-items: flex-start; justify-content: space-between; padding: 0 18px 18px 22px; }
.brand-link { display: flex; flex-direction: column; color: var(--ink); }
.brand-link:hover { text-decoration: none; }
.brand-title { font-family: var(--serif); font-size: 21px; font-weight: 500; letter-spacing: -0.01em; }
.brand-sub { font-size: 12.5px; color: var(--ink3); margin-top: 2px; }
.icon-btn {
  display: inline-flex; align-items: center; justify-content: center;
  width: 34px; height: 34px; border-radius: 9px; border: 1px solid transparent;
  background: transparent; color: var(--ink2); cursor: pointer;
}
.icon-btn:hover { background: var(--accent-soft); color: var(--ink); }

/* ---------------- nav ---------------- */
.nav { padding: 0 10px; }
.nav-chapter { margin: 4px 0 10px; }
.nav-ch-head {
  display: block; padding: 8px 12px 4px; color: var(--ink);
}
.nav-ch-num { display: block; font-size: 10.5px; letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink3); font-weight: 600; }
.nav-ch-title { display: block; font-family: var(--serif); font-size: 16px; line-height: 1.25; }
.nav-list { list-style: none; margin: 2px 0 0; padding: 0; }
.nav-list a {
  position: relative; display: block; padding: 4px 12px 4px 24px; margin: 1px 0;
  border-radius: 8px; color: var(--ink2); font-size: 13.5px; line-height: 1.35;
}
.nav-list a:hover { background: var(--accent-soft); color: var(--ink); text-decoration: none; }
.nav-list a.active { color: var(--accent); background: var(--accent-soft); font-weight: 500; }
.nav-list a.active::before {
  content: ""; position: absolute; left: 10px; top: 50%; width: 6px; height: 6px; margin-top: -3px;
  border-radius: 50%; background: var(--accent);
}
.nav-home { display: block; padding: 6px 12px; margin: 0 0 8px; border-radius: 8px; color: var(--ink2); font-size: 13.5px; }
.nav-home.active { color: var(--accent); background: var(--accent-soft); }
.nav-home:hover { background: var(--accent-soft); text-decoration: none; }

/* ---------------- page ---------------- */
.crumb { font-size: 12px; letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink3); font-weight: 600; margin-bottom: 6px; }
.crumb a { color: var(--ink3); }
h1.title { font-family: var(--serif); font-weight: 500; font-size: 36px; line-height: 1.15; letter-spacing: -0.015em; margin: 0 0 12px; }
.lead { font-size: 16.5px; color: var(--ink2); max-width: 72ch; margin: 0 0 22px; }
.lead p { margin: 0 0 10px; }

.stage {
  background: var(--panel); border: 1px solid var(--hair); border-radius: var(--radius);
  box-shadow: var(--shadow); overflow: hidden;
}
.canvas-wrap { position: relative; width: 100%; }
.canvas-wrap canvas { display: block; width: 100%; touch-action: none; }
.canvas-wrap.orbit canvas { cursor: grab; }
.canvas-wrap.orbit canvas:active { cursor: grabbing; }
.drag-hint {
  position: absolute; right: 10px; bottom: 8px; font-size: 11px; color: var(--ink3);
  background: var(--panel); padding: 1px 7px; border-radius: 6px; opacity: 0.92;
  pointer-events: none; user-select: none; transition: opacity .4s;
}
.drag-hint.gone { opacity: 0; }

/* player */
.player {
  display: flex; align-items: center; gap: 6px; padding: 10px 14px;
  border-top: 1px solid var(--hair);
}
.pbtn {
  display: inline-flex; align-items: center; justify-content: center; flex: none;
  width: 36px; height: 36px; border-radius: 10px; border: 1px solid var(--hair);
  background: var(--panel); color: var(--ink); cursor: pointer;
}
.pbtn:hover { border-color: var(--ink3); }
.pbtn.play { width: 44px; background: var(--ink); color: var(--panel); border-color: var(--ink); }
.pbtn.play:hover { opacity: 0.88; }
.pbtn svg { display: block; }
.scrub { flex: 1; margin: 0 10px; min-width: 60px; }
.ptime { font-family: var(--mono); font-size: 12.5px; color: var(--ink2); min-width: 92px; text-align: right; font-variant-numeric: tabular-nums; white-space: nowrap; }
.pspeed {
  font: 500 12px var(--sans); color: var(--ink2); background: transparent; border: 1px solid var(--hair);
  border-radius: 8px; height: 30px; padding: 0 8px; cursor: pointer; margin-left: 4px;
}
.pspeed:hover { border-color: var(--ink3); color: var(--ink); }

/* sliders */
input[type="range"] { -webkit-appearance: none; appearance: none; width: 100%; height: 22px; background: transparent; margin: 0; cursor: pointer; }
input[type="range"]::-webkit-slider-runnable-track { height: 4px; border-radius: 4px; background: linear-gradient(to right, var(--ink2) var(--pct, 0%), var(--hair) var(--pct, 0%)); }
input[type="range"]::-moz-range-track { height: 4px; border-radius: 4px; background: var(--hair); }
input[type="range"]::-moz-range-progress { height: 4px; border-radius: 4px; background: var(--ink2); }
input[type="range"]::-webkit-slider-thumb { -webkit-appearance: none; width: 16px; height: 16px; border-radius: 50%; background: var(--panel); border: 2px solid var(--ink); margin-top: -6px; }
input[type="range"]::-moz-range-thumb { width: 12px; height: 12px; border-radius: 50%; background: var(--panel); border: 2px solid var(--ink); }
input[type="range"]:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 6px; }

/* controls */
.controls {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 14px 26px;
  padding: 16px 18px 18px; border-top: 1px solid var(--hair);
}
.controls:empty { display: none; }
.ctl label { display: flex; justify-content: space-between; align-items: baseline; font-size: 13px; color: var(--ink2); margin-bottom: 4px; gap: 8px; }
.ctl label .val { font-family: var(--mono); font-size: 12.5px; color: var(--ink); font-variant-numeric: tabular-nums; white-space: nowrap; }
.ctl.wide { grid-column: 1 / -1; }
.seg { display: inline-flex; flex-wrap: wrap; background: var(--bg); border: 1px solid var(--hair); border-radius: 10px; padding: 3px; gap: 2px; }
.seg button {
  font: 500 12.5px var(--sans); color: var(--ink2); background: transparent; border: 0; border-radius: 7px;
  padding: 6px 11px; cursor: pointer; white-space: nowrap;
}
.seg button:hover { color: var(--ink); }
.seg button.on { background: var(--panel); color: var(--ink); box-shadow: 0 1px 2px rgba(0,0,0,0.12); }
.ctl label.toggle { display: inline-flex; justify-content: flex-start; margin: 0; }
.toggle { display: inline-flex; align-items: center; gap: 9px; font-size: 13px; color: var(--ink2); cursor: pointer; user-select: none; padding-top: 6px; }
.toggle input { display: none; }
.toggle .sw { position: relative; width: 32px; height: 18px; border-radius: 10px; background: var(--hair); transition: background .15s; flex: none; }
.toggle .sw::after { content: ""; position: absolute; left: 2px; top: 2px; width: 14px; height: 14px; border-radius: 50%; background: var(--panel); box-shadow: 0 1px 2px rgba(0,0,0,.25); transition: left .15s; }
.toggle input:checked + .sw { background: var(--ink); }
.toggle input:checked + .sw::after { left: 16px; }
.btn {
  font: 500 13px var(--sans); color: var(--ink); background: var(--panel); border: 1px solid var(--hair);
  border-radius: 9px; padding: 7px 12px; cursor: pointer;
}
.btn:hover { border-color: var(--ink3); }

/* readouts */
.readouts {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(170px, 1fr)); gap: 0;
  border-top: 1px solid var(--hair);
}
.readouts:empty { display: none; }
.ro { padding: 10px 18px 12px; border-right: 1px solid var(--hair); }
.ro .k { font-size: 11.5px; color: var(--ink3); letter-spacing: 0.02em; display: flex; align-items: center; gap: 6px; }
.ro .k .dot { width: 8px; height: 8px; border-radius: 50%; display: inline-block; flex: none; }
.ro .v { font-family: var(--mono); font-size: 16px; color: var(--ink); font-variant-numeric: tabular-nums; margin-top: 1px; overflow-wrap: anywhere; }

/* notes */
.notes { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 28px; margin-top: 30px; }
.notes.single { grid-template-columns: minmax(0, 1fr); }
.note h3 { font-size: 11.5px; letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink3); font-weight: 600; margin: 0 0 10px; }
.note ul { margin: 0; padding: 0; list-style: none; }
.note li { position: relative; padding-left: 18px; margin: 0 0 9px; color: var(--ink); max-width: 64ch; }
.note li::before { content: ""; position: absolute; left: 2px; top: 0.62em; width: 6px; height: 6px; border-radius: 50%; background: var(--ink3); }
.note.try li::before { background: var(--accent); border-radius: 2px; transform: rotate(45deg); }
.aside-note { margin-top: 22px; padding: 12px 16px; border-left: 3px solid var(--hair); color: var(--ink2); font-size: 14px; max-width: 80ch; }
.aside-note b { color: var(--ink); font-weight: 600; }

/* prev / next */
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-top: 44px; padding-top: 22px; border-top: 1px solid var(--hair); }
.pager a { display: block; padding: 12px 16px; border: 1px solid var(--hair); border-radius: 12px; background: var(--panel); color: var(--ink); }
.pager a:hover { border-color: var(--ink3); text-decoration: none; }
.pager .dir { display: block; font-size: 11.5px; color: var(--ink3); letter-spacing: 0.06em; text-transform: uppercase; }
.pager .nm { font-family: var(--serif); font-size: 17px; }
.pager .next { text-align: right; grid-column: 2; }
.kbd-hint { margin-top: 14px; font-size: 12px; color: var(--ink3); }
kbd { font-family: var(--mono); font-size: 11px; border: 1px solid var(--hair); border-bottom-width: 2px; border-radius: 5px; padding: 0 5px; background: var(--panel); color: var(--ink2); }

/* home */
.home h1 { font-family: var(--serif); font-weight: 500; font-size: 46px; line-height: 1.08; letter-spacing: -0.02em; margin: 6px 0 16px; }
.home .lead { font-size: 18px; }
.home-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 14px; margin-top: 30px; }
.home-card { border: 1px solid var(--hair); background: var(--panel); border-radius: 14px; padding: 16px 18px; }
.home-card .n { font-size: 11px; letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink3); font-weight: 600; }
.home-card h2 { font-family: var(--serif); font-weight: 500; font-size: 20px; margin: 2px 0 4px; }
.home-card p { margin: 0 0 8px; color: var(--ink2); font-size: 14px; }
.home-card ul { margin: 0; padding: 0; list-style: none; font-size: 13.5px; }
.home-card li { margin: 2px 0; }
.legend { display: flex; flex-wrap: wrap; gap: 8px 18px; margin: 18px 0 0; font-size: 13.5px; color: var(--ink2); }
.legend span { display: inline-flex; align-items: center; gap: 7px; }
.legend i { width: 10px; height: 10px; border-radius: 50%; display: inline-block; }
.cta { display: inline-block; margin-top: 22px; padding: 10px 18px; border-radius: 10px; background: var(--ink); color: var(--panel); font-weight: 500; }
.cta:hover { text-decoration: none; opacity: 0.9; }

/* ---------------- small screens ---------------- */
@media (max-width: 900px) {
  .app { grid-template-columns: minmax(0, 1fr); }
  .sidebar {
    position: fixed; z-index: 30; left: 0; top: 0; bottom: 0; width: 300px; max-width: 86vw;
    transform: translateX(-102%); transition: transform .22s ease;
    box-shadow: 0 0 40px rgba(0,0,0,.2);
  }
  body.nav-open .sidebar { transform: none; }
  .scrim { display: block; position: fixed; inset: 0; z-index: 25; background: rgba(0,0,0,.25); opacity: 0; pointer-events: none; transition: opacity .2s; }
  body.nav-open .scrim { opacity: 1; pointer-events: auto; }
  .topbar {
    display: flex; align-items: center; gap: 8px; position: sticky; top: 0; z-index: 20;
    padding: 8px 12px; background: var(--bg); border-bottom: 1px solid var(--hair);
  }
  .topbar-title { font-family: var(--serif); font-size: 18px; color: var(--ink); }
  .main { padding: 22px 16px 60px; }
  h1.title { font-size: 28px; }
  .home h1 { font-size: 34px; }
  .notes { grid-template-columns: minmax(0, 1fr); gap: 18px; }
  .player { flex-wrap: wrap; padding: 10px; }
  .scrub { order: 10; flex-basis: 100%; margin: 6px 2px 0; }
  .ptime { margin-left: auto; min-width: 0; font-size: 11.5px; }
  .pbtn { width: 32px; height: 32px; border-radius: 9px; }
  .pbtn.play { width: 40px; }
  .pspeed { height: 28px; padding: 0 6px; }
  .controls { grid-template-columns: minmax(0, 1fr); padding: 14px; }
  .readouts { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .ro { padding: 8px 12px 10px; }
  .pager { grid-template-columns: minmax(0, 1fr); }
  .pager .next { grid-column: 1; }
}