设置rem布局

这样设置完成后在PC端1rem是100px，移动端1rem是50px

<script>
      (function (doc, win) {
        var docEl = doc.documentElement,
          resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
          recalc = function () {
            var clientWidth = docEl.clientWidth;
            if (!clientWidth) return;
            if (clientWidth >= 750) {
              docEl.style.fontSize = '100px';
            } else {
              docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
            }
          };
  
        if (!doc.addEventListener) return;
        win.addEventListener(resizeEvt, recalc, false);
        doc.addEventListener('DOMContentLoaded', recalc, false);
      })(document, window);
    </script>