<meta content="target-densitydpi=320,width=640,user-scalable=no" name="viewport"> 

会自动根据dpi320和宽度640的比例，整体页面缩放改变效果


@media (device-height:480px) and (-webkit-min-device-pixel-ratio:2){/* 兼容iphone4/4s */
.class{}
}

@media (device-height:568px) and (-webkit-min-device-pixel-ratio:2){/* 兼容iphone5 */
    .class{}
}


@media (device-height:667px) and (-webkit-min-device-pixel-ratio:2){/* 兼容iphone6 */
    .class{}
}

@media (device-height:736px) and (-webkit-min-device-pixel-ratio:2){/* 兼容iphone6 Plus */
    .class{}
} 


div{max-width:640px;min-width:320px;margin:0 auto;width:100%;height:100%;}