Shrinking menu on scroll

shrinkmenu.js

(function($){
  $(function(){
    var lastScrollTop = 0, delta = 5;
    $(window).scroll(function(event){
       var st = $(this).scrollTop();
       if( $(window).scrollTop() > 200 ) {
         if(Math.abs(lastScrollTop - st) <= delta)
            return;
         
         if (st > lastScrollTop){
            $("#main-header").addClass("animated slideUp");
            $("#main-header").removeClass("slideDown");
         } else {
            $("#main-header").removeClass("slideUp");
            $("#main-header").addClass("animated slideDown");
         }
         lastScrollTop = st;
      }
    });
	});
})(jQuery);

style.css

.animated {
  -webkit-animation-duration: .5s;
  -moz-animation-duration: .5s;
  -o-animation-duration: .5s;
  animation-duration: .5s;
  -webkit-animation-fill-mode: both;
  -moz-animation-fill-mode: both;
  -o-animation-fill-mode: both;
  animation-fill-mode: both
}

@-webkit-keyframes slideDown {
  0% {
    -webkit-transform: translateY(-120px);
  }

  100% {
    -webkit-transform: translateY(0);
  }
}

@-moz-keyframes slideDown {
  0% {
    -moz-transform: translateY(-120px);
  }

  100% {
    -moz-transform: translateY(0);
  }
}

@-o-keyframes slideDown {
  0% {
    -o-transform: translateY(-120px);
  }

  100% {
    -o-transform: translateY(0);
  }
}

@keyframes slideDown {
  0% {
    transform: translateY(-120px);
  }

  100% {
    transform: translateY(0);
  }
}

.animated.slideDown {
  -webkit-animation-name: slideDown;
  -moz-animation-name: slideDown;
  -o-animation-name: slideDown;
  animation-name: slideDown;
}

@-webkit-keyframes slideUp {
  0% {
    -webkit-transform: translateY(0);
  }

  100% {
    -webkit-transform: translateY(-120px);
  }
}
@-moz-keyframes slideUp {
  0% {
    -moz-transform: translateY(0);
  }

  100% {
    -moz-transform: translateY(-120px);
  }
}
@-o-keyframes slideUp {
  0% {
    -o-transform: translateY(0);
  }

  100% {
    -o-transform: translateY(-120px);
  }
}
@keyframes slideUp {
  0% {
    transform: translateY(0);
  }

  100% {
    transform: translateY(-120px);
  }
}

.animated.slideUp {
  -webkit-animation-name: slideUp;
  -moz-animation-name: slideUp;
  -o-animation-name: slideUp;
  animation-name: slideUp;
}