根据移动设备的分辨率，设置rem根fontSize大小

<script>
  (function (window, document) {
    function resize() {
      if (/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)) {
        var ww = window.innerWidth
        if (ww > window.screen.width) {
          window.requestAnimationFrame(resize)
        } else {
          if (ww > 750) {
            ww = 750
          }
          document.documentElement.style.fontSize = ww * 100 / 750 + 'px'
        }
      }
    }

    resize();

    window.addEventListener('resize', resize);
    window.addEventListener('pageshow', function (e) {
      if (e.presisted) {
        resize();
      }
    });
  })(window, document);
</script>