一、兼容性最好-的伪元素方法:after

给浮动的父盒子提供一个伪元素

.father:after {
      content: " ";
      display: block;
      height: 0;
      clear: both;
      visibility: hidden;
    }

二、额外标签法

<div class="father">
    <div class="sonbox1"></div>
    <div class="sonbox2"></div>
    <div style="clear: both;"></div>
  </div>