<div class="container">
  <div class="left"></div>
  <div class="right"></div>
  <div class="main"></div>
</div>
*{
    margin: 0;
    padding: 0;
  }
  .left{
    float: left;
    height: 200px;
    width: 100px;
    margin-right: 20px;
    background: red;
  }
  .right{
    float: right;
    width: 200px;
    height: 200px;
    margin-left: 20px;
    background: green;
  }
  .main{
    height: 200px;
    overflow: hidden; /* 触发BFC */
    background: blue;
  }

External CSS

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External JavaScript

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