body {
    background: url(/Assets/BGs/check6-b.gif);
}

#content {
    background: var(--AEROglass);
    backdrop-filter: blur(2px);
    -webkit-backdrop-filter: blur(6px); /* ? And here's where I found out this exists... */
    box-shadow: 0 0 40px var(--AEROshadow);
}