code: def _apply_base_theme(app):
      
  
      if QT_VERSION < (5,):
          app.setStyle('plastique')
      else:
          app.setStyle('Fusion')
  
      with open(_STYLESHEET) as stylesheet:
          app.setStyleSheet(stylesheet.read())
docs: Apply base theme to the application.
  
          Args:
              app (QApplication): QApplication instance.