CODE EXAMPLE FOR CSS

animation background css

@keyframes gradient {
    0% {
        background-position: 0% 50%;
    }
    50% {
        background-position: 100% 50%;
    }
    100% {
        background-position: 0% 50%;
    }
}
body{
    width: 100vw;
    height: 100vh;
}
div{
    transition: all .3s ease-in-out;
    background: linear-gradient(-45deg, #ee7752, #e73c7e, #23a6d5, #23d5ab);
    background-size: 400% 400%;
    animation: gradient 15s ease infinite;
    height: 500px;
    width: 500px;
}