标签：des style blog http color io os ar java
经常设计页面时用到三层DIV，头DIV与脚DIV一般固定高度，而中间层DIV根据内容的多少，高度不定，我们经常希望但内容很少时，脚DIV保持在底部，当内容很多时，脚DIV被中间内容挤到下面，但仍然始终保持在底部。
position有四个参数：static | relative | absolute | fixed
position:static，意味元素没有被定位，元素会出现在文档本该出现位置，是页面元素默认的定位的方式，一般无需指定，除非想要覆盖之前设置的定位。
position:relative,很明白，相对元素本该位置的偏移量
#nav{ position:relative; top:15px; left:20px; }
position:absolute,这时候元素已经脱离了文档，文档中已经没有自己的本该的位置了，但我们可以通过left、bottom、left和right来规定其在文档中位置。
#nav{ postion:absolute; botton:0px; }
我们知道万物都是相对的，元素进行上面设置了后就保证nav元素始终保持在底部了呢？nav元素离botton为0px,是哪个为参照物呢，是父级元素还还是浏览器呢，其实这里分为两种情况：
如果父级元素（父级元素的父级、父级的父级的父级......）设置postion时，则子元素此时相对的是父级的，所以当内容过多时，脚DIV不能被挤到底部去。
如果父级元素（父级元素的父级、父级的父级的父级......）没有设置postion时，则子元素此时相对的是浏览器的，所以当内容过少时，脚DIV不能被调到底部去。
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} function indexFunc(){ window.document.getElementById("about").style.display="none"; } </script> </head> <body> <div id="header"> <h1 class="blogtitle"> <a href="http://www.cnblogs.com/chenyuming507950417/">助你软件工作室</a> </h1> <p class="desc">二十八年，我用青春修行</p> </div> <div id="ddnav"> <div id="nav"> <ul class="nav"> <li><a href="#" onclick="indexFunc();">主页</a></li> </ul> <ul class="nav"> <li><a href="#" onclick="aboutFunc();">关于</a></li> </ul> </div> </div> <div id="top"> </div> <div class="content"> <div id="post-e0a6ac53-c204-4919-9fda-2021397c40b8"> <p><p class="MsoNormal" style="margin-bottom: 7.5pt; text-align: center; mso-pagination: widow-orphan;" align="center"> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">麦子，你是怎样长进我的眼睛</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span> </strong><strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你站立的土地一直站着我的双脚</span> </strong><strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我们同根而生，是伙伴</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">只是我比你在泥土上住得更久</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我一辈子是生活的奴隶，为了生计</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">一年一次，我用锋利的镰刀收割</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你的麦芒对着天，从没刺伤我</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">为让我拿镰的手有更多的力气</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你在一盘磨里走很长的路</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">把自己碾的粉身碎骨</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我是在饥饿时学会了感恩</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">端起一碗饭就想你熟了的肤色</span> </strong><strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">想起在泥土上来回行走的季节</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">麦子，你年年回来吧，我年年爱你</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"></span></strong> </p></p> </div> <div id="about" style="display:none;"> <p><p class="MsoNormal" style="margin-bottom: 7.5pt; text-align: center; mso-pagination: widow-orphan;" align="center"> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">麦子，你是怎样长进我的眼睛</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span> </strong><strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你站立的土地一直站着我的双脚</span> </strong><strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我们同根而生，是伙伴</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">只是我比你在泥土上住得更久</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我一辈子是生活的奴隶，为了生计</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">一年一次，我用锋利的镰刀收割</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你的麦芒对着天，从没刺伤我</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">为让我拿镰的手有更多的力气</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">你在一盘磨里走很长的路</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">把自己碾的粉身碎骨</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">我是在饥饿时学会了感恩</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">端起一碗饭就想你熟了的肤色</span> </strong><strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">想起在泥土上来回行走的季节</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"><br /> </span></strong> <strong><span style="font-size: 14pt; font-family: 宋体;" lang="ZH">麦子，你年年回来吧，我年年爱你</span></strong> <strong><span style="font-size: 14pt; font-family: Arial;" lang="EN-US"></span></strong> </p></p> </div> </div> <div id="footer"> </div> <div id="footerbox"> <div class="footer"> <a href="http://www.cnblogs.com/chenyuming507950417/">助你软件工作室</a> 二十八年，我用青春修行 © Copyright 2014 </div> </div> <body> </html>
（1）http://blog.davidqiu.com/post/2013-06-17/40051753968
（2）http://www.cnblogs.com/ahjesus/archive/2011/11/26/2263986.html
标签：des style blog http color io os ar java
原文地址：http://www.cnblogs.com/chenyuming507950417/p/4003651.html
