<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<div class="container">
<div class="row">
<h2>Create your snippet's HTML, CSS and Javascript in the editor tabs</h2>
</div>
</div>
jQuery(window).scroll(function() {
var scroll = jQuery(window).scrollTop();
if (scroll >= 300) {
jQuery(".header-bg").addClass("darkHeader");
} else {
jQuery(".header-bg").removeClass("darkHeader");
}
});
