语法缩写如下：
background ： [background-color] | [background-image] | [background-position][/background-size] | [background-repeat] | [background-attachment] | [background-clip] | [background-origin],...
注意：用逗号隔开每组background的缩写值；如果有size值，需要紧跟position并且用"/"隔开；分解写法时，background-color只能设置一个。
例如：
background:url(./image.jpg) no-repeat left top / 200px 70px,url(./image.jpg) no-repeat right bottom / 150px 60px;
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>多重背景</title>
<style type="text/css">
.demo {
300px;
height: 140px;
border: 1px solid #999;
background:url(http://static.mukewang.com/static/img/logo_index.png) no-repeat left top / 200px 70px,
url(http://static.mukewang.com/static/img/logo_index.png) no-repeat right bottom / 150px 60px;
}
</style>
</head>
<body>
<div class="demo"></div>
</body>
</html>