'Fills the panel background using QPalette.'

def paintEvent(self, event):

    if (self.isVisible() and (self.position != self.Position.FLOATING)):
        self._background_brush = QBrush(QColor(self.editor.sideareas_color))
        self._foreground_pen = QPen(QColor(self.palette().windowText().color()))
        painter = QPainter(self)
        painter.fillRect(event.rect(), self._background_brush)
