Make element (nav) fixed on scoll (CSS position: sticky).

HTML

<div class="image"></div>
<nav id="nav">
    <h1>NAVIGATION BAR</h1>
</nav>
<dl>
    <dt>A</dt>
    <dd>Andrew W.K.</dd>
    <dd>Apparat</dd>
    <dd>Arcade Fire</dd>
    <dd>At The Drive-In</dd>
    <dd>Aziz Ansari</dd>
</dl>
<div class="image"></div>

CSS

nav {
    position: sticky;
    top: -1px;
}

.image {
    
    height:1000px;
}