利用 CSS3 判断手机是横屏还是竖屏

@media screen and (orientation: portrait) {
  /*竖屏 css*/
} 
@media screen and (orientation: landscape) {
  /*横屏 css*/
}

 或者分开引入

<link rel="stylesheet" media="all and (orientation:portrait)" href="portrait.css">
<link rel="stylesheet" media="all and (orientation:landscape)" href="landscape.css">