100vh workaround

gistfile1.js

    var mediaQueryList = window.matchMedia('(orientation: portrait)');

    function setMaxHeight (mediaQueryList) {
      var vh = window.innerHeight;
      var vw = window.innerWidth;
      var header = document.querySelector('.site-header');

      if (mediaQueryList.matches) {
        header.style.height = Math.max(vh, vw);
      } else {
        header.style.height = Math.min(vh, vw);
      }
    }

    setMaxHeight(mediaQueryList);
    mediaQueryList.addListener(setMaxHeight);