html, body { margin: 0; height: 100%; background: #0b0f17; }
body { display: grid; place-items: center; overflow: hidden; }
/* Scale the fixed 640x480 canvas to fill the frame at 4:3, on any screen. */
canvas { display: block; width: min(100vw, calc(100vh * 4 / 3)); height: auto; aspect-ratio: 4 / 3; touch-action: none; }