code: def paintEvent(self, event):
          
          opt = QtWidgets.QStyleOption()
          opt.initFrom(self)
          painter = QtGui.QPainter(self)
          self.style().drawPrimitive(QtWidgets.QStyle.PE_Widget, opt, painter, self)
          painter.end()
docs: Reimplementation of paintEvent to allow for style sheets
              See: http://qt-project.org/wiki/How_to_Change_the_Background_Color_of_QWidget