body::before {
    content:""; /* required for ::before */
    position:fixed; /* don't scroll with page */
    z-index:-100; /* place behind elements on page */
    width:100%;
    height:100%;
    background-color:#8d8d8d;
    background-image: 
    radial-gradient(circle farthest-side at top right, transparent, #f1d67c), radial-gradient(ellipse farthest-corner at 0% 100%, transparent, #f390f3);
    animation:bg-change 10s infinite;
}

@keyframes bg-change {
0%, 100% {
    filter:hue-rotate(0deg);
}
50% {
    filter:hue-rotate(-45deg);
}
}