纯css实现背景颜色渐变动画，代码及效果图如下。

body {
    width: 100vw;
    height: 100vh;
    color: #fff;
    background: linear-gradient(-45deg, #EE7752, #E73C7E, #23A6D5, #23D5AB);
    background-size: 400% 400%;
    -webkit-animation: Gradient 15s ease infinite;
    -moz-animation: Gradient 15s ease infinite;
    animation: Gradient 15s ease infinite;
}

@-webkit-keyframes Gradient {
    0% {
        background-position: 0% 50%
    }
    50% {
        background-position: 100% 50%
    }
    100% {
        background-position: 0% 50%
    }
}

@-moz-keyframes Gradient {
    0% {
        background-position: 0% 50%
    }
    50% {
        background-position: 100% 50%
    }
    100% {
        background-position: 0% 50%
    }
}

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

效果图：

这世上从来就没有横空出世的运气，只有不为人知的努力。