垂直居中案例
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
.conner{
position:fixed;
background:url(http://img.zcool.cn/community/012a765542c1af0000019ae9c8493e.jpg) 50% 50% no-repeat #fff;
z-index:9999;
width:100%;
height:100%;
top:0;
left:0;
}
</style>
</head>
<body>
<div class="conner"></div>
</body>
</html>
