title: QGtkStyle could not resolve GTK
body: <p>I have a series of apps installed in Ubuntu 18.04 using Anaconda. They run just fine, but the menus appear as blank.<a href="https://i.stack.imgur.com/4X2u7.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4X2u7.png" alt="gtk apps not displaying the menus"></a></p>
  
  <p>Some of these apps are:</p>
  
  <ul>
  <li>Spyder</li>
  <li>Orange 3</li>
  <li>qtconsole</li>
  </ul>
  
  <p>For all of them I obtain the same error when I execute them:</p>
  
  <p><code>QGtkStyle could not resolve GTK. Make sure you have installed the proper libraries.</code></p>
  
  <p>I have been trying to sort it for hours without success.</p>
  
  <p>Any idea of how to fix this?</p>