/* Checkers — 8×8 board with American draughts discs & kings. Container-relative only (rule 35). */
.chk-board { display: grid; grid-template-columns: repeat(8, 1fr); width: min(100%, 440px); aspect-ratio: 1; border: 2px solid var(--border); border-radius: var(--radius-sm); overflow: hidden; }
.chk-sq { position: relative; border: none; padding: 0; display: flex; align-items: center; justify-content: center; cursor: pointer; background: var(--surface); }
.chk-sq.is-dark { background: color-mix(in srgb, var(--text-primary) 18%, var(--surface)); }
.chk-sq.is-sel { outline: 3px solid var(--brand); outline-offset: -3px; z-index: 1; }
.chk-sq.is-focus { outline: 2px dashed var(--text-primary); outline-offset: -2px; }
.chk-sq.is-hint::after { content: ""; width: 32%; height: 32%; border-radius: 50%; background: #16a34a; opacity: 0.85; }
.chk-sq.is-must { box-shadow: inset 0 0 0 2px var(--brand); }
.chk-disc { width: 76%; height: 76%; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-family: var(--font-mono); font-size: clamp(0.75rem, 2.8cqw, 1.05rem); font-weight: 800; pointer-events: none; box-shadow: inset 0 -3px 0 rgba(0, 0, 0, 0.28), 0 1px 2px rgba(0, 0, 0, 0.2); }
.chk-disc.is-r { background: #ef4444; color: #fff; }
.chk-disc.is-b { background: #1e293b; color: #f8fafc; border: 1px solid rgba(255, 255, 255, 0.18); }