title: bootstrap 4 navbar border bottom color
body: <p>A lot of searching, but without result. How to change the border-bottom color of the navbar in Bootstrap 4</p>
  
  <pre><code>&lt;nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-dark justify-content-center"&gt;
  ....
  &lt;/nav&gt;
  </code></pre>