(function() {
    document.addEventListener('DOMContentLoaded', function () {
      var html = document.documentElement;
      var windowWidth = html.clientWidth;
      html.style.fontSize = windowWidth / 7.5 + 'px';
      //等价于html.style.fontSize = windowWidth / 750 * 100 + 'px';
   }, false);
})();

二倍图  750