解决方法
你应该把它们漂浮在清除的容器中.
例：
https://jsfiddle.net/W74Z8/504/
一个干净的实现是“clearfix hack”.这是Nicolas Gallagher的版本：
/**
* For modern browsers
* 1. The space content is one way to avoid an Opera bug when the
* contenteditable attribute is included anywhere else in the document.
* Otherwise it causes space to appear at the top and bottom of elements
* that are clearfixed.
* 2. The use of `table` rather than `block` is only necessary if using
* `:before` to contain the top-margins of child elements.
*/
.clearfix:before,.clearfix:after {
content: " "; /* 1 */
display: table; /* 2 */
}
.clearfix:after {
clear: both;
}
/**
* For IE 6/7 only
* Include this rule to trigger hasLayout and contain floats.
*/
.clearfix {
*zoom: 1;
}
