<!-- 动态计算font-size - rem -->
   <script  charset="utf-8">
     (function (doc, win) {
         var docEl = doc.documentElement,
         resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
         recalc = function () {
             var clientWidth = docEl.clientWidth;
             if (!clientWidth) return;
             docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
             docEl.getElementsByTagName("body")[0].style.fontSize = docEl.style.fontSize;
         };

         if (!doc.addEventListener) return;
         win.addEventListener(resizeEvt, recalc, false);
         doc.addEventListener('DOMContentLoaded', recalc, false);
         
     })(document, window);

   </script>