change nav background color on scroll css without bootstrap

1$(function () {
2  $(document).scroll(function () {
3    var $nav = $(".navbar-fixed-top");
4    $nav.toggleClass('scrolled', $(this).scrollTop() > $nav.height());
5  });
6});

1<script>
2  $(document).ready(function()
3  $(window).scroll(function(){
4   var scroll = $(window).scrollTop();
5     if(scroll>50){
6      $("#nav").css("background", "#555");
7       }
8       else {
9      $("#nav").css("background", "transparent");
10       }
11      })
12   })
13</script>