title: Add custom css class to WordPress Gallery
body: <p>I would like to add a custom css class to the native WordPress gallery. For example, this one outputs the following HTML:</p>
  
  <pre><code>&lt;div id="gallery-2" class="gallery galleryid-1715 gallery-columns-4 gallery-size-thumbnail"&gt;
  </code></pre>
  
  <p>I'd like to just add in a custom class of <code>iwmp</code>.</p>
  
  <p>What's the best way of doing this? I was hoping for a non JS solution. Thanks</p>
  
  <p>EDIT: Answered my question below.</p>