html {
    background: url('bg.png') center center;
}
#page {
    box-shadow: #000 0 0 1em;
    min-height: 90vh;
}

#menu {
    text-align: center;
}

@media(min-width: 100em) { html { background-size: 512px; } }
@media(min-width: 200em) { html { background-size: 1024px; } }