<script type="text/javascript">

     var addStyleLink = function(href){

     var head = document.getElementsByTagName('head')[0];

     var styleLink = document.createElement('link');

     styleLink.setAttribute('rel','stylesheet');

     styleLink.setAttribute('href',href);

     head.appendChild(styleLink);

     }

     // 苹果手机采用CSS1

     if(/iphone/i.test(navigator.userAgent)){

         addStyleLink('css/css1.css');   //这里路径要写对

     }

     // 安卓手机采用CSS2

     if(/android/i.test(navigator.userAgent)){

         addStyleLink('css/css2.css');

     }

 </script>