:root {
  --bg: #f4f1ea;
  --surface: #e4dfd2;
  --text: #26231d;
  --muted: #6b655a;
  --tile: #fffdf8;
  --tile-home: #dcebd4;
  --accent: #b5532b;
  --accent-text: #ffffff;
  --border: #bdb6a4;
  --gap: 6px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1c1a17;
    --surface: #2b2823;
    --text: #ece7db;
    --muted: #a39d8f;
    --tile: #3a362f;
    --tile-home: #3b4a37;
    --accent: #e0805a;
    --accent-text: #1c1a17;
    --border: #4a453b;
  }
}

* { box-sizing: border-box; }

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

main {
  max-width: 30rem;
  margin: 0 auto;
  padding: 1.5rem 16px 3rem;
}

h1 {
  margin: 0 0 0.25rem;
  font-size: 1.75rem;
  letter-spacing: 0.02em;
}

.stats {
  display: flex;
  gap: 1rem;
  align-items: baseline;
  min-height: 3em;
  margin-bottom: 0.75rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.stats strong { color: var(--text); font-variant-numeric: tabular-nums; }

.board {
  --n: 3;
  position: relative;
  width: 100%;
  aspect-ratio: 1;
  background: var(--surface);
  border: var(--gap) solid var(--surface);
  border-radius: 10px;
}

.tile {
  position: absolute;
  top: 0;
  left: 0;
  width: calc(100% / var(--n));
  height: calc(100% / var(--n));
  padding: calc(var(--gap) / 2);
  border: 0;
  background: none;
  font: inherit;
  color: inherit;
  cursor: pointer;
  transform: translate(calc(var(--c) * 100%), calc(var(--r) * 100%));
  transition: transform 0.14s ease-out;
  /* Tile faces are drawn by ::before so the gap between tiles needs no maths. */
  font-size: clamp(1rem, calc(16vw / var(--n)), 2.25rem);
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  z-index: 0;
  isolation: isolate;
}

.tile::before {
  content: "";
  position: absolute;
  inset: calc(var(--gap) / 2);
  background: var(--tile);
  border: 1px solid var(--border);
  border-radius: 8px;
  z-index: -1;
}

.tile.home::before { background: var(--tile-home); }
.tile.hint::before { outline: 3px solid var(--accent); outline-offset: 1px; }
.tile:focus-visible::before { outline: 3px solid var(--text); outline-offset: 1px; }

.controls, .options {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 0.75rem;
  align-items: center;
  margin-top: 1rem;
}

button:not(.tile) {
  min-height: 2.5rem;
  padding: 0 1.1rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  color: var(--text);
  font: inherit;
  cursor: pointer;
}

button:not(.tile):hover:not(:disabled) { border-color: var(--accent); }
button:not(.tile):disabled { opacity: 0.5; cursor: default; }
#solve { background: var(--accent); border-color: var(--accent); color: var(--accent-text); }

select {
  min-height: 2.5rem;
  margin-left: 0.4rem;
  padding: 0 0.5rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  color: var(--text);
  font: inherit;
}

fieldset {
  display: flex;
  gap: 0.9rem;
  margin: 0;
  padding: 0 0.75rem 0.25rem;
  border: 1px solid var(--border);
  border-radius: 6px;
}

legend { padding: 0 0.3rem; color: var(--muted); font-size: 0.8rem; }

label:has(input:disabled) { color: var(--muted); }

.help {
  margin-top: 1.5rem;
  color: var(--muted);
  font-size: 0.875rem;
}

@media (prefers-reduced-motion: reduce) {
  .tile { transition: none; }
}

.nav { margin: 0 0 1rem; font-size: 0.9rem; }
.nav a { color: var(--accent); }