问下如何让两个浮动元素行高自动相等？
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><link href="main_style.css" rel="stylesheet" rev="stylesheet" type="text/css" media="all" /><link href="menu.css" rel="stylesheet" rev="stylesheet" type="text/css" media="all" /><title>无标题文档</title></head><body> <div id="mainbox"> <div id="header"><h1>W3School.com.cn</h1></div> <div id="sidebar"> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> <p>"Never increase, beyond what is necessary, the number of entities required to explain anything." William of Ockham (1285-1349)</p> </div> <div id="content"><h2>Free Web Building Tutorials</h2> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> <p>W3School.com.cn - The Largest Web Developers Site On The Net!</p> </div> <div id="footer">Copyright 2008 by YingKe Investment. </div> </div> </body></html>
改成这样试试一下，因为都是内部的DIV，不属于浮动层，DIV会随着数据的增加变高，很明显，你左右2部分的P标签不一样多，建议设置成固定值，然后overflow:hidden;这样垂直方向就不会被挤开。
