body { margin: 0; min-height: 100vh; display: grid; place-items: center;
       font: 16px/1.5 system-ui, sans-serif; background: #f7f7f5; color: #222; }
main { padding: 16px; text-align: center; }
@media (prefers-color-scheme: dark) { body { background: #1b1b1b; color: #eee; } }