内容垂直、水平居中

 CSS
.amdin_img{z-index:-99; position:fixed;}
.amdin_main{ position:absolute;   top:50%;  left:50%;  width:580px;  height:600px; margin-top:-300px; margin-left:-290px; line-height:30px;font-size:16px;   text-align:center;z-index:-1;filter:alpha(opacity:30);opacity:0.3; background:#333;}
.amdin_nr{ position:absolute;top:50%;left:50%;width:200px;height:100px; margin-top:-50px; margin-left:-100px; border:1px solid red; line-height:30px;font-size:16px;text-align:center;z-index:99} 


Html
<div class="amdin_img"><img style="position:fixed;" src="images/admin-bg.jpg"  height="100%" width="100%" /></div>
<div class="amdin_main"></div>
<div class="amdin_nr">78978</div>