title: Bootstrap4 adding scrollbar to div
body: <p>I am using <a href="http://v4-alpha.getbootstrap.com/components/navs/#stacked-pills" rel="noreferrer">stacked pills</a> inside a <code>div</code>. The problem is, sometimes the <code>div</code> contains a lot of pills. How can I add a scrollbar for it?</p>
  
  <pre><code>&lt;div class="row col-md-2"&gt;
  &lt;ul class="nav nav-pills nav-stacked"&gt;
    &lt;li class="nav-item"&gt;
      &lt;a class="nav-link active" href="#"&gt;Active&lt;/a&gt;
    &lt;/li&gt;
    &lt;li class="nav-item"&gt;
      &lt;a class="nav-link" href="#"&gt;Link&lt;/a&gt;
    &lt;/li&gt;
    &lt;li class="nav-item"&gt;
      &lt;a class="nav-link" href="#"&gt;Link&lt;/a&gt;
    &lt;/li&gt;
    &lt;li class="nav-item"&gt;
      &lt;a class="nav-link disabled" href="#"&gt;Disabled&lt;/a&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Can I add a class for the div to make stacked pills scrollable?</p>