初学css便遇难题，求大神，求指导，各种求（如下）
代码1：<div align="center">
<link href="style/nm.css" rel="stylesheet" type="text/css" />
<div alt="初学css就遇难题，求大神，求指导，各种求（如下）" />
[解决办法]
显示呀！
<!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" />
<title>无标题文档</title>
<style type="text/css">
.main
{
width:1003px;
height:2000px;
overflow:hidden;
background:white;
}
.z{
width:1003px;
height:800px;
overflow:hidden;
background:red;
position:relative;
top:90px;
}
.top {
width: 1003px;
height: 90px;
overflow: hidden;
background-color:blue;
}
</style>
</head>
<body>
<div class="main">
<div class="top"></div>
<div class="z">是不显示吗
</div>
</div>
</div>
</body>
</html>
