最后foot中为什么要设置清除浮动：clear:both啊。感觉前面没有设置浮动啊，而且我把清除浮动的去掉，还是达到了同样的效果。
嘿嘿，感谢收听
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我是这样写的，所以我要清除浮动。
body{ margin:0; padding:0; font-size:30px; color:#fff}
.top{height：100px;background:gray;}
.main{height:500px;background:red;}
.left{height:500px;width:19%;background:blue;float:left;}
.right{height:500px;width:79%;background:green;float:right;}
.foot{height:100px;background:orange;clear:both;}
我觉得你都没有用浮动，那你有什么浮动要清除吗？clear是设置一个元素的侧面是否允许其它的浮动元素，既然没有设置浮动就不需要清除了。