去网上着了好久都没找到，后来想到了cacl计算属性才解决
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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<style>
html,body{
height:100%;
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height: 100%;
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.ani {
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height: 100px;
background: #000;
animation: a 2s linear;
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left: 0;
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@keyframes a {
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<body>
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</html>完~