GradientAnimator

.css-selector {
    background: linear-gradient(42deg, #6385f2, #4de9f2, #b03ef0, #37f5ab);
    background-size: 800% 800%;
    -webkit-animation: bg-gradient 39s ease infinite;
    -moz-animation: bg-gradient 39s ease infinite;
    -o-animation: bg-gradient 39s ease infinite;
    animation: bg-gradient 39s ease infinite;
}
@-webkit-keyframes bg-gradient {
    0%{background-position:90% 0%}