body {
    animation: changeBg 10s infinite
    alternate linear;

}
@keyframes changeBg{
    0% {
        background: #6699FF;

    }
    25% {
        background: #60d394;

    }
    50% {
        background: #aaf683;

    }
    75% {
        background: #ffd97d;

    }
    100% {
        background: #6699FF;

    }
}