@media screen and (max-width: 768px) {
    .main-header { flex-direction: column; gap: 10px; }
    .main-nav { display:flex; gap:10px; justify-content:center; width:100%; flex-wrap:wrap; margin-top:10px; }
    .main-nav .nav-item { margin-left:0; }
    .center-box { padding: 10px; align-items:flex-start; margin-top:20px; }
    .inventory-grid { gap: 2px !important; }
}