响应式设计：根据不同设备引不同css样式

<link rel="stylesheet" media="screen and (max-width:600px)" href="small.css" type="text/css" />

<link rel="stylesheet" media="screen and (min-width:900px)" href="big.css" type="text/css"  />

body{
    background-color: #fff;
}
@media screen and (max-width: 600px) {
     body{
         background-color: #ccc;
     }
 } 

body{
    background-color: #fff;
}
@media screen and (min-width: 900px) {
     body{
         background-color: #ccc;
     }
 }