网页背景图片固定切自适应浏览器高度宽度

例如：

body {
padding: 0px;
margin-top: 70px; 
margin-right: auto;
margin-left: auto;
background-attachment: fixed;
background-repeat: no-repeat;
background-image: url(http://pic.chinafilm.com/upimg/main/images/12.jpg);
background-position: center top;
font-family: "宋体";
font-size: 12px;
line-height: 20px;
margin-bottom: 0px;
}