============== go to top =========================
    var gttBtn = document.getElementById("gtt");
    gttBtn.style.display = "none";
    gttBtn.addEventListener('click', function () {
      if (window.document.documentMode) {
        document.documentElement.scrollTop = 0;
      } else {
        scrollToTop(250);
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    });

    function scrollToTop(scrollDuration) {
      var scrollStep = -window.scrollY / (scrollDuration / 15);
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        if (window