css控制div置顶置底的例子
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<title>why?</title>
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http://www.w3css.com/allnews.asp?id=990
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<style type="text/css" media="screen">
<!--
* {margin:0;padding:0;}
body {margin:0 auto;font:12px/20px tahoma Simsun Arial;color:#fff;background-color:#FFF;text-align:center;}
.aaa{ width:150px; background:Blue;position:absolute;left:0;top:0; }
.bbb{ width:150px; background:Blue;position:absolute;right:0;top:0; }
.ccc{ width:150px; position:absolute; top:100%;left:0; margin-top:-20px; background:Blue;}
.ddd{ width:150px; position:absolute; top:100%;right:0; margin-top:-20px; background:Blue;}
.aa{ width:50px; position:fixed; background:Black; _position:absolute;_top:expression(eval(document.documentElement.scrollTop));z-index:1000;left:0;top:0; }
.bb{ width:50px; position:fixed; background:Black; _position:absolute;_top:expression(eval(document.documentElement.scrollTop));z-index:1000;right:0;top:0; }
.a{ color:#000; }
-->
</style>
</head>
<body>
<div class="aaa">AAA</div>
<div class="bbb">BBB</div>
<div class="aa">A</div>
<div class="bb">B</div>
<div class="a">
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A层和B层会随滚动条移动永久置顶
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</div>
<div class="ccc">CCC</div>
<div class="ddd">DDD</div>
</body>
</html>
