var designWidth = document
  .getElementsByTagName("head")[0]
  .getAttribute("design-width");

function font_size(devwidth) {
  _size();

  window.onresize = function () {
    _size();
  };

  function _size() {
    var deviceWidth = document.documentElement.clientWidth;
    if (deviceWidth >= devwidth) deviceWidth = devwidth;
    document.documentElement.style.fontSize =
      deviceWidth / (devwidth / 100) + "px";
  }
}

var media = document.createElement("style");
media.innerHTML =
  "@media screen and (min-width:" +
  designWidth +
  "px){.center{width:" +
  designWidth +
  "px !important;margin-left:-" +
  designWidth / 2 +
  "px !important;left:50% !important;}.fixed-right{right:calc((100% - 750px)/2)}}";
document.getElementsByTagName("head")[0].appendChild(media);

window.onload = font_size(designWidth);