<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="header">
<h1 class="header_logo">Resizing Fixed Header</h1>
</div>
<div class="offset">
<p>Scroll down to initiate resizing of the page header.</p>
</div>
<script>
window.addEventListener('scroll', function() {
navbarScroll();
});
function navbarScroll() {
var y = window.scrollY;
if (y > 10) {
var header = document.getElementsByClassName('header')[0];
header.classList.add('small');
} else if (y < 10) {
var header = document.getElementsByClassName('header')[0];
header.classList.remove('small');
}
}
</script>
