移动端使用CSS或JS判断横屏和竖屏的讲解

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

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

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

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

//判断手机横竖屏状态：
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); 
//移动端的浏览器一般都支持window.orientation这个参数，通过这个参数可以判断出手机是处在横屏还是竖屏状态。

//判断屏幕方向
if(window.orientation==90||window.orientation==-90){
  alert("横屏状态！")
}
//监听屏幕方向
window.onorientationchange = function(){ 
  switch(window.orientation){ 
    case -90: 
    case 90: 
      alert("横屏:" + window.orientation);
    case 0: 
    case 180: 
       alert("竖屏:" + window.orientation);
    break; 
  } 
} 

<!--css媒介查询判断-->
@media (orientation: portrait) { } 横屏
@media (orientation: landscape) { }竖屏 

transform: rotate(90deg);