用一张图片作为网页的背景，能让这个图片不管是在普通显示器还是宽屏显示器上都能全屏显示

<html>
<head>
<title> </title>
<style type="text/css">
#div1
{
position: fixed;
top: 0;
left: 0;
bottom: 0;
right: 0;
z-index: -1;
}
#div1 img
{
height: 100%;
width: 100%;
border: 0;
}
</style>
</head>
<body>
<div id="div1">
<img src="http://www.xieguang133.com/wp-content/uploads/baidu_pic/other_site/img_baidu_bg.jpg" alt="" />
</div>
</body>
</html>