body{margin:0;font-family:-apple-system,Arial;background:#111827;color:#fff}
header{background:#e10600;padding:18px;text-align:center}
nav{display:flex;overflow:auto;background:#1f2937}
button{flex:1;padding:12px;border:0;background:#1f2937;color:#fff}
button:hover{background:#e10600}
main{padding:16px}
.page{display:none;background:#fff;color:#111;padding:16px;border-radius:12px}
.active{display:block}