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  <title>Document</title>
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    .title {
      color: #333;
      line-height: 2;
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    .title span {
      background: linear-gradient(to right,#ff9a9e 0%, #fad0c4 99%, #fad0c4 100%) no-repeat right bottom;
      background-size: 0 2px;
      transition: background-size 1300ms;
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    .title span:hover {
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      background-size: 100% 2px;
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  <h2 class="title">
    <span>
      十年后，你会发现css是你永远学不会的语言
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