:root {
  --bg: #f4f5f7;
  --fg: #15181d;
  --muted: #586271;
  --card: #ffffff;
  --line: #dde1e7;
  --accent: #2457d6;
  --accent-fg: #ffffff;
  --danger: #b3261e;
  --warn: #8a5a00;
  --body: #15171b;
  --unset: #b4bbc5;
  --stage: #e8ebf1;
  --c-U: #f4f4f2;
  --c-R: #d6342c;
  --c-F: #1f9d55;
  --c-D: #f2c500;
  --c-L: #f28a1a;
  --c-B: #1f5fd1;
  --p: 3px;
  --g: 3px;
  --face-gap: 8px;
  /* page padding + card padding + borders + scrollbar */
  --gutter: 80px;
  --s: min(46px, calc((100vw - var(--gutter) - 4 * (2 * var(--p) + 2 * var(--g)) - 3 * var(--face-gap)) / 12));
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0e1116;
    --fg: #eef1f5;
    --muted: #9aa5b4;
    --card: #171b21;
    --line: #29303a;
    --accent: #7aa0ff;
    --accent-fg: #0a1020;
    --danger: #ff8f86;
    --warn: #f2c14e;
    --unset: #4b5460;
    --stage: #2b3340;
  }
}

@media (max-width: 520px) {
  :root {
    --p: 2px;
    --g: 2px;
    --face-gap: 6px;
    --gutter: 56px;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}

main {
  max-width: 920px;
  margin: 0 auto;
  padding: 20px 16px 56px;
}

header { margin-bottom: 20px; }
h1 { margin: 4px 0 6px; font-size: clamp(1.6rem, 4vw, 2.2rem); letter-spacing: -0.02em; }
h2 { margin: 0 0 6px; font-size: 1.1rem; }
.lede { margin: 0; color: var(--muted); max-width: 60ch; }
.back { color: var(--muted); text-decoration: none; font-size: 0.9rem; }
.back::before { content: "← "; }
.back:hover { color: var(--accent); }
a { color: var(--accent); }

.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 18px;
  margin-bottom: 18px;
}

.hint, .meta { margin: 0 0 12px; color: var(--muted); font-size: 0.92rem; max-width: 70ch; }

/* paint palette */
.palette { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 14px; }
.swatch {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 12px 6px 8px;
  border: 2px solid var(--line);
  border-radius: 999px;
  background: var(--card);
  color: var(--fg);
  font: inherit;
  font-size: 0.9rem;
  cursor: pointer;
}
.swatch i {
  width: 22px;
  height: 22px;
  border-radius: 6px;
  border: 1px solid rgba(0, 0, 0, 0.4);
  background: var(--c);
}
.swatch[aria-pressed="true"] { border-color: var(--accent); box-shadow: 0 0 0 2px color-mix(in srgb, var(--accent) 30%, transparent); }

/* net */
.net-wrap { overflow-x: auto; padding: 2px 0 6px; }
.net {
  display: grid;
  grid-template-columns: repeat(4, max-content);
  grid-template-areas:
    ". u . ."
    "l f r b"
    ". d . .";
  gap: var(--face-gap);
  width: max-content;
  margin: 0 auto;
  touch-action: none;
  user-select: none;
}
.face {
  display: grid;
  grid-template-columns: repeat(3, var(--s));
  grid-auto-rows: var(--s);
  gap: var(--g);
  padding: var(--p);
  background: var(--body);
  border-radius: 9px;
  outline: 3px solid transparent;
  outline-offset: 2px;
  transition: outline-color 0.15s;
}
.face[data-face="U"] { grid-area: u; }
.face[data-face="L"] { grid-area: l; }
.face[data-face="F"] { grid-area: f; }
.face[data-face="R"] { grid-area: r; }
.face[data-face="B"] { grid-area: b; }
.face[data-face="D"] { grid-area: d; }
.face.next { outline-color: var(--accent); }

.sticker {
  width: var(--s);
  height: var(--s);
  padding: 0;
  border: 0;
  border-radius: 5px;
  background: var(--unset);
  color: #fff;
  font: 600 calc(var(--s) * 0.4) / 1 system-ui, sans-serif;
  cursor: pointer;
  background-image: repeating-linear-gradient(135deg, transparent 0 5px, rgba(0, 0, 0, 0.07) 5px 10px);
}
.sticker[data-c] { background-image: none; }
.sticker[data-c="U"] { background-color: var(--c-U); color: #222; }
.sticker[data-c="R"] { background-color: var(--c-R); }
.sticker[data-c="F"] { background-color: var(--c-F); }
.sticker[data-c="D"] { background-color: var(--c-D); color: #222; }
.sticker[data-c="L"] { background-color: var(--c-L); }
.sticker[data-c="B"] { background-color: var(--c-B); }
.sticker.center { cursor: default; box-shadow: inset 0 0 0 2px rgba(0, 0, 0, 0.35); }
.sticker:focus-visible { outline: 3px solid var(--accent); outline-offset: 1px; }
.net:not(.letters) .sticker { font-size: 0; }

/* controls */
.toolbar { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin-top: 14px; }
button, select {
  font: inherit;
  font-size: 0.95rem;
  color: var(--fg);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 8px 14px;
}
button { cursor: pointer; }
button:hover:not(:disabled) { border-color: var(--accent); }
button:disabled { opacity: 0.5; cursor: not-allowed; }
button.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); font-weight: 600; }
button:focus-visible, select:focus-visible, summary:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
label.inline { display: inline-flex; align-items: center; gap: 8px; color: var(--muted); font-size: 0.9rem; margin-left: 4px; }

.status { min-height: 1.5em; margin: 12px 0 0; color: var(--muted); }
.status.error { color: var(--danger); }
.status.warn { color: var(--warn); }
.status.busy::before {
  content: "";
  display: inline-block;
  width: 0.9em;
  height: 0.9em;
  margin-right: 8px;
  vertical-align: -0.1em;
  border: 2px solid var(--line);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* solution */
.moves { display: flex; flex-wrap: wrap; gap: 6px; list-style: none; margin: 0 0 12px; padding: 0; }
.chip {
  min-width: 2.7em;
  padding: 6px 10px;
  font: 600 0.95rem ui-monospace, SFMono-Regular, Menlo, monospace;
  text-align: center;
}
.chip.done { opacity: 0.45; }
.chip.current { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); opacity: 1; }

/* a trigger: its chips boxed together with the name underneath */
.moves .group {
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding: 5px 7px 4px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: color-mix(in srgb, var(--accent) 8%, var(--card));
  max-width: 100%;
}
.moves .group.active { border-color: var(--accent); }
.moves { align-items: flex-start; }
/* line single chips up with the chips inside a box (its padding plus border) */
.moves > li:not(.group) { padding-top: 6px; }
.group-chips { display: flex; flex-wrap: wrap; gap: 6px; }
.group-name { font-size: 0.78rem; line-height: 1.25; color: var(--muted); }

.table-wrap { overflow-x: auto; }
.triggers { border-collapse: collapse; margin-top: 4px; }
.triggers th, .triggers td { padding: 6px 14px 6px 0; text-align: left; vertical-align: top; border-top: 1px solid var(--line); }
.triggers th { font-weight: 600; color: var(--fg); white-space: nowrap; }
.triggers code { font: 600 0.9rem ui-monospace, SFMono-Regular, Menlo, monospace; color: var(--fg); white-space: nowrap; }
.now { min-height: 3em; margin: 0; font-size: 1.05rem; }

/* 3D player */
.stage {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin: 0 0 12px;
}
.view { margin: 0; }
.view figcaption { margin-top: 2px; text-align: center; color: var(--muted); font-size: 0.85rem; }

.cube-view {
  --cs: clamp(22px, calc((100vw - 140px) / 8), 54px);
  --hl: #fff;
  position: relative;
  height: calc(var(--cs) * 5.6);
  perspective: calc(var(--cs) * 22);
  background: var(--stage);
  border: 2px solid transparent;
  border-radius: 12px;
  transition: border-color 0.2s;
}
.cube-view.active { border-color: var(--accent); }

.scene, .cubie, .slot {
  position: absolute;
  left: 50%;
  top: 50%;
  width: 0;
  height: 0;
  transform-style: preserve-3d;
}
.slot {
  left: 0;
  top: 0;
  transform: translate3d(calc(var(--x) * var(--cs)), calc(var(--y) * var(--cs)), calc(var(--z) * var(--cs)));
}
.cubie { left: 0; top: 0; }

.f, .plate {
  position: absolute;
  width: var(--w);
  height: var(--w);
  left: calc(var(--w) / -2);
  top: calc(var(--w) / -2);
  backface-visibility: hidden;
}
.f { --w: var(--cs); --h: calc(var(--cs) / 2); background: var(--body); }
.plate { --w: calc(var(--cs) * 3); --h: calc(var(--cs) * 1.5 + 2px); display: none; pointer-events: none; }
.o-F { transform: translateZ(var(--h)); }
.o-B { transform: rotateY(180deg) translateZ(var(--h)); }
.o-R { transform: rotateY(90deg) translateZ(var(--h)); }
.o-L { transform: rotateY(-90deg) translateZ(var(--h)); }
.o-U { transform: rotateX(90deg) translateZ(var(--h)); }
.o-D { transform: rotateX(-90deg) translateZ(var(--h)); }

.tile {
  position: absolute;
  inset: 6%;
  border-radius: 14%;
  background: var(--unset);
}
.tile[data-c="U"] { background: var(--c-U); }
.tile[data-c="R"] { background: var(--c-R); }
.tile[data-c="F"] { background: var(--c-F); }
.tile[data-c="D"] { background: var(--c-D); }
.tile[data-c="L"] { background: var(--c-L); }
.tile[data-c="B"] { background: var(--c-B); }
.tile.center::after {
  content: attr(data-l);
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  font: 700 calc(var(--cs) * 0.42) / 1 system-ui, sans-serif;
  color: rgba(0, 0, 0, 0.45);
}
.tile.covered::after { display: none; }

.plate.on {
  display: block;
  border-radius: calc(var(--cs) * 0.2);
  background: rgba(255, 255, 255, 0.16);
  box-shadow: inset 0 0 0 3px #fff, inset 0 0 0 5px #111, 0 0 0 2px #111;
}
.plate svg { display: block; width: 100%; height: 100%; }
.plate .halo path, .plate .halo polygon { fill: #111; stroke: #111; stroke-width: 13; stroke-linecap: round; stroke-linejoin: round; }
.plate .halo path { fill: none; }
.plate .ink path, .plate .ink polygon { fill: #fff; stroke: #fff; stroke-width: 6; stroke-linecap: round; stroke-linejoin: round; }
.plate .ink path { fill: none; }
.plate text {
  fill: #fff;
  stroke: #111;
  stroke-width: 4px;
  paint-order: stroke;
  font: 700 25px system-ui, sans-serif;
  text-anchor: middle;
  dominant-baseline: central;
}

.about { color: var(--muted); font-size: 0.95rem; max-width: 70ch; }
.about summary { cursor: pointer; color: var(--fg); }

[hidden] { display: none !important; }

@media (max-width: 520px) {
  main { padding-left: 12px; padding-right: 12px; }
  .card { padding: 12px; }
}