title: What is the equivalent of the Bootstrap 3 'btn-default' class in Bootstrap 4?
body: <p>There was a nice button created by <code>btn-default</code> in Bootstrap 3.</p>
  
  <pre><code>&lt;a class="btn btn-default"&gt;link&lt;/a&gt;
  </code></pre>
  
  <p>Is there an equivalent in Bootstrap 4?</p>