body{margin:0;font-family:Arial;background:#efefef}
body.dark{background:#161616;color:#fff}
header{background:#b30000;color:#fff;padding:15px;text-align:center}
.menu{display:flex}
.menu button{flex:1;padding:15px}
.page{display:none;padding:20px}
.page.active{display:block}
.cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(180px,1fr));gap:12px}
.card{background:#fff;padding:20px;border-radius:10px}
body.dark .card{background:#2d2d2d}