*{box-sizing:border-box}body{margin:0;font-family:system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;color:#111;background:#f6f6f7}
.container{max-width:980px;margin:0 auto;padding:24px}
.lead{color:#555}
h1{margin:.2em 0 0.2em 0;font-size:clamp(24px,4vw,36px)}
h2{margin:1.2em 0 .5em 0}
.cta{display:flex;gap:12px;margin-top:12px}
.btn{display:inline-block;padding:10px 14px;border-radius:10px;background:#111;color:#fff;text-decoration:none}
.btn.outline{background:#fff;color:#111;border:1px solid #ddd}
.cards{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}
.card{padding:18px;border-radius:12px;border:1px solid #e6e6e8;background:#fff;text-decoration:none;color:#111;text-align:center}
#sudoku-board{max-width:560px;margin:1rem 0}