当动画为 25% 及 50% 时改变背景色，然后当动画 100% 完成时再次改变 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    div {
      width: 100px;
      height: 100px;
      background: red;
      animation: myfirst 5s;
      -moz-animation: myfirst 5s;
      /* Firefox */
      -webkit-animation: myfirst 5s;
      /* Safari and Chrome */
      -o-animation: myfirst 5s;
      /* Opera */
    }

    @keyframes myfirst {
      0% {
        background: red;
      }
      25% {
        background: yellow;
      }
      50% {
        background: blue;
      }
      100% {
        background: green;
      }
    }

    @-moz-keyframes myfirst
    /* Firefox */

    {
      0% {
        background: red;
      }
      25% {
        background: yellow;
      }
      50% {
        background: blue;
      }
      100% {
        background: green;
      }
    }

    @-webkit-keyframes myfirst
    /* Safari and Chrome */

    {
      0% {
        background: red;
      }
      25% {
        background: yellow;
      }
      50% {
        background: blue;
      }
      100% {
        background: green;
      }
    }

    @-o-keyframes myfirst
    /* Opera */

    {
      0% {
        background: red;
      }
      25% {
        background: yellow;
      }
      50% {
        background: blue;
      }
      100% {
        background: green;
      }
    }
  </style>
</head>
<body>

  <div></div>

  <p><b>注释：</b>当动画完成时，会变回初始的样式。</p>

  <p><b>注意:</b> 该实例在 Internet Explorer 9 及更早 IE 版本是无效的。</p>

</body>
</html>
        