HiddenFixedHeaderMenu.js

<script>
  
  //Hidden Fixed header v1.1
  
  //Replace ID below with your box ID
  var boxToFix = '#lp-pom-box-88';
  
  //Set the number of pixels to scroll before showing the header
  var scrollPositionToShowHeader = 50;
  
  var boxParent = $(boxToFix).parent();
  var boxClone = $(boxToFix).clone();
      
  $(boxClone).appendTo(boxParent).css({"position":"fixed", "left":"0", "top":"0", "width":"100%", "z-index":"899"}).children().remove();

  $(boxToFix).css({"position":"fixed", "left":"auto", "top":"0px", "width":"100%", "z-index":"999", "border-style":"none none none none", "border-width":"0px", "background":"none"});
  
  showOrHideHeader();
  
  function showOrHideHeader() {
    var currentPositionFromTop = $(window).scrollTop();
    
    if (currentPositionFromTop > scrollPositionToShowHeader) {
      $(boxToFix).show();
      $(boxClone).show();
    } else {
      $(boxToFix).hide();
      $(boxClone).hide();
    }
  }
  
  $(window).scroll(function() {
    showOrHideHeader();
  });
  
</script>