title: Apply different QSS stylesheet for custom QT class
body: <p>I am using a qss stylesheet for my gui. It works well but I would like to define a different style sheet for my custom widget. 
  By example, <code>QPushbutton</code>'s style works well but I would like to apply a different style for <code>MyQPushButton</code> (extends from QPushButton).</p>
  
  <p>I tried something like this :</p>
  
  <pre><code>MyQPushButton
  {
      color: #dcdcdc;
      // some code here
  }
  
  QPushButton
  {
      color: #b1b1b1;
      // some code here
  }
  </code></pre>
  
  <p>But <code>QPushButton</code>'s style has been applied on <code>MyQPushButton</code>.
  How to override this behavior ? </p>