How to create a animated background for the site page?

Site URL: https://www.stevenwalbrick.com

Im trying to get an animated background similar to this page (https://www.seanhalpin.xyz/fun). I want it to stay at the top and just move at the top like it is on that page. Need the css for it if thats possible.

Thanks

You can use this example code to Website Tools > Custom CSS. Replace color with your desired color

body {
 background: linear-gradient(-45deg, #ee7752, #e73c7e, #23a6d5, #23d5ab);
    background-size: 400% 400%;
    animation: gradient 15s ease infinite;
    overflow-x: hidden;
}
.header-background-solid {
    background-color: transparent !important;
}
.section-background, .section-border, section {
  background-color: transparent !important;
}
@keyframes gradient {
    0% {
        background-position: 0% 50%;
    }
    50% {
        background-position: 100% 50%;
    }
    100% {
        background-position: 0% 50%;
    }
}