title: Stylesheet QmainWindow does not work on pyqt5, only qt designer preview
body: <p>stylesheet Qt designer:</p>
  <pre><code>QMainWindow {
                  
      background-image: url(:/tela/app_imagens/kawaii-1546834.png);
                  background-repeat: no-repeat; 
                  background-position: center;
   }
  </code></pre>
  <p>In the preview of the qt designer the stylesheet works normally:</p>
  <p><a href="https://i.stack.imgur.com/OItdp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OItdp.png" alt="qt" /></a></p>
  <p>however when running the application nothing appears:</p>
  <p><a href="https://i.stack.imgur.com/gFNBE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gFNBE.png" alt="app" /></a></p>