body { margin:0; font-family: sans-serif; background:#f4f4f4;}
header{background:#111827;color:#fff;text-align:center;padding:1rem;}
.controls{display:flex;flex-wrap:wrap;gap:.5rem;padding:1rem;background:#e5e7eb;}
.controls button, .controls select, .controls input{padding:.4rem .6rem;font-size:1rem;}
#viewer{width:100%;height:80vh;background:#fff;}