不定高度实现居中显示
<!DOCTYPE html>
<html>
<meta name="name" content="content" charset='utf-8'>
<head>
<title>网页居中</title>
</head>
<style type="text/css" media="screen">
*{margin:0;padding: 0;}
.al{width: 800px;height: 600px;margin: 30px auto;position: relative;border:1px solid red;}
.par{position: absolute;top:50%;left:50%;}
.chd{background: green;position: relative;top:-50%;left:-50%;}
.ul{width: 600px;height:400px;margin: 10px auto;border:1px solid blue; }
.ul li{width: 50px;height: 30px;border:1px solid red;text-align: center;line-height: 30px;list-style-type: none;float:left;margin: 20px 0 0 20px;}
</style>
<body>
<div class="al">
<div class="par">
<div class="chd">
我要居中我要居中
</div>
</div>
</div>
</body>
</html>
第二种方法
<!DOCTYPE html>
<html>
<meta name="name" content="content" charset='utf-8'>
<head>
<title>网页居中</title>
</head>
<style type="text/css" media="screen">
*{margin:0;padding: 0;}
.al{width: 800px;height: 600px;margin: 30px auto;}
.par{width: 800px;height: 600px;border:1px solid red;display: table-cell;text-align: center;vertical-align: middle;}
.chd{background: green;display: inline-block;}
</style>
<body>
<div class="al">
<div class="par">
<div class="chd">
我要居中我要居中
</div>
</div>
</div>
</body>
</html>
