window.onload = function () {
  getRem(750, 100)
};
window.onresize = function () {
  getRem(750, 100)
};
function getRem(pwidth, prem) {
  var html = document.getElementsByTagName("html")[0];
  var oWidth = document.body.clientWidth || document.documentElement.clientWidth;
  console.log(oWidth / pwidth * prem)
  html.style.fontSize = oWidth / pwidth * prem + "px";
}