1 <link rel="stylesheet" media="screen and (min-device-width : 320px) and (max-device-width: 480px)" href="iphone.css" />
2 <link rel="stylesheet" media="screen and (min-device-width : 768px) and (max-device-width : 1024px)" href="ipad.css" />
3 media对各种设备的判断，分离css文件,易于维护

1 viewport设置
2 <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">