移动端适配（rem）方案

    (function (doc, win) {
      let docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function () {
          let clientWidth = docEl.clientWidth;
          if (!clientWidth) return;
          docEl.style.fontSize = 100 * (clientWidth / 375) + 'px';
        };

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