(function (doc, win) {
  var docEl = doc.documentElement;
  var resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';

  function recalc() {
    var clientWidth = docEl.clientWidth;
    if (!clientWidth) return;
    if (clientWidth >= 750) {
      docEl.style.fontSize = '100px';
    }else{
      docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
    }
  };
  recalc();
  win.addEventListener(resizeEvt, recalc, false);
})(document, window);