新手div的嵌套不会排列整齐
]#headertop{width:800px;height:20px;background:#CCFF77;}
#headertop ul{list-style:none;}
#headertop ul li{float:left;margin:10px auto 10px 0}
#headerbottom{width:800px;height:80px;background:#CCFF44}
#headerbottomleft{width:100px;height:80px;text-align:left;background:#CCFF55}
#headerbottomcenter{width:400px;height:70px;background:#CCFF33}
#headerbottomright{width:300px;height:70px;background:#CCFF66}
<div id="header">
<!--页面头部-->
<div id="headertop">
<ul>
<li>亲，欢迎来淘宝！请</li>
</ul>
</div>
<div id="headerbottom">
<div id="headerbottomleft"></div>
<div id="headerbottomcenter"> </div>
<div id="headerbottomright"></div>
</div>
</div>