围住浮动元素的三种方法

当有浮动元素时：

<section>
<img src="images/rubber_duck2.jpg">
<p>It's fun to float.</p>
</section>
<footer> Here is the footer element that runs across the bottom of the
page.</footer>

section {border:1px solid blue; margin:0 0 10px 0;}
img {float:left;}
footer {border:1px solid red;}

有三种方法可以解决这个问题：

为父元素添加overflow:hidden

section {border:1px solid blue; margin:0 0 10px 0; overflow:hidden;}
img {float:left;}
p {border:1px solid red;}

同时浮动父元素

section {border:1px solid blue; float:left; width:100%;}
img {float:left;}
footer {border:1px solid red; clear:left;}

添加非浮动的清除元素

<section>
<img src="images/rubber_duck.jpg">
<p>It's fun to float.</p>
<div class="clear_me"></div>
</section>
<footer> Here is the footer element…</footer>

section {border:1px solid blue;}
img {float:left;}
.clear_me {clear:left;}
footer {border:1px solid red;}

如果不想添加这个纯表现型元素，我再告诉你一个用css来添加这个清除元素的方法。首先给section添加一个类

<section class="clearfix">
<img src="images/rubber_duck.jpg">
<p>It's fun to float.</p>
</section>
<footer> Here is the footer element…</footer>

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