jQuery(document).ready(function($){
  var didScroll;
  var lastScrollTop = 0;
  var delta = 5;
  var navbarHeight = $('nav').outerHeight(true);

  $(window).scroll(function(event) { didScroll = true; });

  setInterval(function() {
    if (didScroll) {
    hasScrolled();
    didScroll = false;
  }
 }, 0);

function hasScrolled() {
 if($( window ).width() > 768) {
   var st = $(this).scrollTop();
 if (Math.abs(lastScrollTop - st) <= delta)
   return;
 if (st > lastScrollTop) {
    // Scroll Down
        $('#screen-nav').removeClass('nav-down').addClass('nav-up');
   } else {
        $('#screen-nav').removeClass('nav-up').addClass('nav-down');
   }

  }
    lastScrollTop = st;
  }

});

#screen-nav {
  position: fixed;
  top: 0; left: 0; right: 0;
 }

#screen-nav.nav-up { top: -100px; }
#screen-nav.nav-down { top: 0; }