<script>
        function Rem() {
          var docEl = document.documentElement,
            oSize = docEl.clientWidth / 7.5;
          if (oSize > 100) {
            oSize = 100; //  限制rem值   640 / 6.4 =100
          }
          docEl.style.fontSize = oSize + ‘px‘;
        }
        window.addEventListener(‘resize‘, Rem, false);
        Rem();
  </script>