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 { width: 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>
