:root {--region-line:#475569;} :root[data-theme=dark] {--region-line:#cbd5e1;}
@media(prefers-color-scheme:dark) {:root:not([data-theme=light]) {--region-line:#cbd5e1;}}
#board {grid-template-columns:repeat(4,minmax(0,1fr));gap:0;} .cell {display:grid;place-items:center;border-radius:0;border-color:var(--region-line);padding:0;font-size:1.7rem;font-weight:400;}
.cell.given {font-weight:800;background:var(--bg);} .cell.invalid {box-shadow:inset 0 0 0 2px var(--error);} .cell.selected {outline:3px solid #2563eb;outline-offset:-4px;} .cell:disabled {opacity:1;}
#numbers {--count:5;} #numbers button {min-width:44px;}
@media(max-width:360px) {main {width:calc(100% - 16px);} .cell {font-size:1.5rem;}}