Bootstrap 4 Scrollspy
<!-- The scrollable area -->
<body data-spy="scroll" data-target=".navbar" data-offset="50">
<!-- The navbar - The <a> elements are used to jump to a section in the scrollable area -->
<nav class="navbar navbar-expand-sm bg-dark navbar-dark fixed-top">
...
<ul class="navbar-nav">
<li><a href="#section1">Section 1</a></li>
...
</nav>
<!-- Section 1 -->
<div id="section1">
<h1>Section 1</h1>
<p>Try to scroll this page and look at the navigation bar while scrolling!</p>
</div>
...
</body>