.s-board {
  --n: 9;
  --s-thick: var(--text);
  --s-thin: color-mix(in srgb, var(--text) 16%, var(--surface));
  --s-peer: color-mix(in srgb, var(--game) 9%, var(--surface));
  --s-same: color-mix(in srgb, var(--game) 26%, var(--surface));
  --s-sel: color-mix(in srgb, var(--game) 38%, var(--surface));
  container-type: inline-size;
  width: 100%;
  aspect-ratio: 1;
  display: grid;
  grid-template-columns: repeat(var(--n), 1fr);
  grid-template-rows: repeat(var(--n), 1fr);
  border: 2.5px solid var(--s-thick);
  border-radius: 8px;
  overflow: hidden;
  background: var(--surface);
}
.s-cell {
  position: relative; display: flex; align-items: center; justify-content: center; min-width: 0; min-height: 0;
  border-right: 1px solid var(--s-thin); border-bottom: 1px solid var(--s-thin);
  font-size: calc(100cqw / var(--n) * .56); line-height: 1; font-variant-numeric: tabular-nums;
  color: var(--game); font-weight: 550; cursor: pointer; transition: background-color .08s;
}
.s-cell.s-lc { border-right: 0; }
.s-cell.s-lr { border-bottom: 0; }
.s-cell.s-br { border-right: 2px solid var(--s-thick); }
.s-cell.s-bb { border-bottom: 2px solid var(--s-thick); }
.s-cell.s-given { color: var(--text); font-weight: 750; }
.s-cell.s-peer { background: var(--s-peer); }
.s-cell.s-same { background: var(--s-same); }
.s-cell.s-sel { background: var(--s-sel); }
.s-cell.s-bad { color: var(--danger); }
.s-cell.s-bad:not(.s-given)::after {
  content: ""; position: absolute; inset: 0; pointer-events: none;
  background: color-mix(in srgb, var(--danger) 12%, transparent);
}
@media (hover: hover) { .s-cell:not(.s-sel):hover { background: color-mix(in srgb, var(--game) 16%, var(--surface)); } }

/* Pencil marks: 3×3 for 9×9, 3×2 for 6×6. */
.s-notes {
  position: absolute; inset: 1px; display: grid;
  grid-template-columns: repeat(3, 1fr); grid-auto-rows: 1fr;
  color: var(--muted); font-weight: 600; font-size: calc(100cqw / var(--n) * .26);
}
.s-notes span { display: flex; align-items: center; justify-content: center; line-height: 1; }
.s-cell.s-note-hit .s-notes { color: var(--text); }

/* Number pad. */
.s-pad { width: min(600px, calc(100vw - 32px)); display: flex; flex-direction: column; gap: 8px; user-select: none; -webkit-user-select: none; }
.s-digits { display: grid; grid-template-columns: repeat(var(--n), 1fr); gap: clamp(3px, 1.2vw, 8px); }
.s-key {
  position: relative; display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 1px;
  min-width: 0; height: clamp(46px, 13vw, 60px); padding: 0; border-radius: 10px; cursor: pointer;
  border: 1px solid var(--line); background: var(--surface); color: var(--game); font: inherit;
  touch-action: manipulation; transition: background .12s, transform .05s;
}
.s-key:hover:not(:disabled) { background: color-mix(in srgb, var(--game) 10%, var(--surface)); }
.s-key:active:not(:disabled) { transform: scale(.95); }
.s-key-d { font-size: clamp(1.25rem, 5.5vw, 1.6rem); font-weight: 700; line-height: 1; }
.s-key-c { font-size: .68rem; font-weight: 600; color: var(--muted); line-height: 1; }
.s-key.s-done { opacity: .38; cursor: default; }
.s-key.s-done .s-key-c { color: var(--good); }
.s-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; }
.s-act { padding: 9px 12px; touch-action: manipulation; }
.s-act.s-on { background: var(--game); border-color: var(--game); color: #fff; }
.s-toggle { font-size: .7rem; font-weight: 800; letter-spacing: .04em; padding: 1px 6px; border-radius: 999px; background: var(--surface-2); color: var(--muted); }
.s-act.s-on .s-toggle { background: rgba(255, 255, 255, .25); color: #fff; }
.s-pad.s-locked { opacity: .55; pointer-events: none; }