//根据设计稿750宽度
(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) {
        clientWidth = 750
      }
      docEl.style.fontSize = 100 * (clientWidth / 750) + 'px'
    };
  win.addEventListener(resizeEvt, recalc, false);
  doc.addEventListener('DOMContentLoaded', recalc, false)
})(document, window);