特效 css3 持续动作的渐变背景

html,body{
    margin:;
    padding:;
    height: 100%;
    width: 100%;
    background: linear-gradient(125deg,#2c3e50,#27ae60,#2980b9,#e74c3c,#8e44ad);
    background-size: 400%;
    animation: my 15s infinite;
}

@keyframes my{
    0%{
        background-position: 0% 50%;
    }
    50%{
        background-position: 100% 50%;
    }
    100%{
        background-position: 0% 50%;
    }
}