判断横屏竖屏（三种）

　　<link rel="stylesheet" media="all and (orientation:portrait)" href="portrait.css" rel="external nofollow" > //引用竖屏的CSS
　　<link rel="stylesheet" media="all and (orientation:landscape)" href="landscape.css" rel="external nofollow" > //引用横屏的CSS

@media (orientation: portrait ){
 //竖屏CSS 
}
@media ( orientation: landscape ){
 //横屏CSS 
}

window.addEventListener("onorientationchange" in window ? orientationchange" : "resize", function() {
  if (window.orientation === 180 || window.orientation === 0) { 
   alert('竖屏状态！');
  } 
  if (window.orientation === 90 || window.orientation === -90 ){ 
   alert('横屏状态！');
  } 
 }, false);