<div class="test1"></div>
<div class="test2"></div>
.test1{
  width: 100px;
  height: 100px;
  float: left;
  background: red;
}
.test2{
  width: 200px;
  height: 200px;
  background: yellow;
/*  如果形成 BFC，就不会重叠了  */
  display: flex;
}

External CSS

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External JavaScript

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