Instead of having a separate scroll for the side navbar, I would prefer to have it scroll along with the main body. This way, when you scroll through the main content, the additional side navbar information will also be displayed.
For an example, you can check out this link: https://jsfiddle.net/wzcya8b9/3/
HTML
<div class="sidenav">
<a href="#about">About</a>
<a href="#services">Services</a>
<a href="#clients">Clients</a>
<a href="#contact">Contact</a>
<a href="#about">About</a>
<a href="#services">Services</a>
<a href="#clients">Clients</a>
</div>
<div class="main">
<h2>Sidebar</h2>
<p>This sidebar is of full height (100%) and always shown.</p>
<p>Scroll down the page to see the result.</p>
</div>
</body>
CSS
.sidenav {
height: 100%;
width: 160px;
position: fixed;
z-index: 1;
top: 0;
left: 0;
background-color: #111;
overflow-x: hidden;
padding-top: 20px;
}
.sidenav a {
padding: 6px 8px 6px 16px;
text-decoration: none;
font-size: 25px;
color: #818181;
display: block;
}
.main {
margin-left: 160px; /* Same as the width of the sidenav */
font-size: 28px; /* Increased text to enable scrolling */
padding: 0px 10px;
}