Just a quick test in https://www.gradient-animator.com/

Gradient Background Animation

background: linear-gradient(44deg, #c8461f, #bdc81f, #36c81f, #1fc8b3, #1f57c8, #a21fc8, #c81f2d);
background-size: 1400% 1400%;

-webkit-animation: AnimationName 36s ease infinite;
-moz-animation: AnimationName 36s ease infinite;
animation: AnimationName 36s ease infinite;

@-webkit-keyframes AnimationName {
    0%{background-position:0% 99%}
    50%{background-position:100% 2%}
    100%{background-position:0% 99%}
}
@-moz-keyframes AnimationName {
    0%{background-position:0% 99%}
    50%{background-position:100% 2%}
    100%{background-position:0% 99%}
}
@keyframes AnimationName { 
    0%{background-position:0% 99%}
    50%{background-position:100% 2%}
    100%{background-position:0% 99%}
}