$(window).scroll(function () {
   var scrollTop = $(window).scrollTop();
   if (scrollTop > 50){
    $('.all').addClass("fixednav").stop().animate({  top: 0 },  300);
   
    $('#header').css({"z-index":1000});
   }else{
    $('.all').css({"top":'-100px'}).removeClass("fixednav").stop ().animate({  top: "0px" }, 300);
    
    $('#header').css({"z-index":99});
   }
  });