Sticky Navigation

  // Sticky Navigation
  $(window).on('scroll',function() {    
   var scroll = $(window).scrollTop();
   if (scroll < 40) {
    $(".sticky").removeClass("scroll-header");
   }else{
    $(".sticky").addClass("scroll-header");
   }
  });

  $("a[href='#top']").click(function() {
  $("html, body").animate({ scrollTop: 0 }, "slow");
  return false;
});

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Add sticky class to header - <header class="sticky">

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In CSS
header.sticky.scroll-header {
    position: fixed;
    left: 0;
    right: 0;
    background: #87509c;
}">