• 利用 border-radius 生成椭圆
• 并不是利用旋转的椭圆本身生成波浪效果，而是利用它去切割背景，产生波浪的效果。

HTML：

<h2>波浪动画</h2>

SCSS：

body {
    position: relative;
    align-items: center;
    min-height: 100vh;
    background-color: rgb(118, 218, 255);
    overflow: hidden;

    &:before, &:after {
        content: "";
        position: absolute;
        left: 50%;
        min-width: 300vw;
        min-height: 300vw;
        background-color: #fff;
        animation-name: rotate;
        animation-iteration-count: infinite;
        animation-timing-function: linear;
    }

    &:before {
        bottom: 15vh;
        border-radius: 45%;
        animation-duration: 10s;
    }

    &:after {
        bottom: 12vh;
        opacity: .5;
        border-radius: 47%;
        animation-duration: 10s;
    }
}

@keyframes rotate {
    0% {
        transform: translate(-50%, 0) rotateZ(0deg);
    }
    50% {
        transform: translate(-50%, -2%) rotateZ(180deg);
    }
    100% {
        transform: translate(-50%, 0%) rotateZ(360deg);
    }
}

h2 {
    position: relative;
    color: #333;
    z-index: 10;
    text-align: center;
    height: 100vh;
    line-height: 140vh;
    font-size: 8vw;
    text-shadow: 3px 3px 2px #999;
}