Paints the background for the dock toolbar.
        
        :param      event | <QPaintEvent>

def paintEvent(self, event):
        """
        Paints the background for the dock toolbar.
        
        :param      event | <QPaintEvent>
        """
        x = 1
        y = 1
        w = self.width()
        h = self.height()
        
        clr_a = QColor(220, 220, 220)
        clr_b = QColor(190, 190, 190)
        
        grad = QLinearGradient()
        grad.setColorAt(0.0, clr_a)
        grad.setColorAt(0.6, clr_a)
        grad.setColorAt(1.0, clr_b)
        
        # adjust the coloring for the horizontal toolbar
        if self.position() & (self.Position.North | self.Position.South):
            h = self.minimumPixmapSize().height() + 6
            
            if self.position() == self.Position.South:
                y = self.height() - h
                grad.setStart(0, y)
                grad.setFinalStop(0, self.height())
            else:
                grad.setStart(0, 0)
                grad.setFinalStart(0, h)
        
        # adjust the coloring for the vertical toolbar
        if self.position() & (self.Position.East | self.Position.West):
            w = self.minimumPixmapSize().width() + 6
            
            if self.position() == self.Position.West:
                x = self.width() - w
                grad.setStart(x, 0)
                grad.setFinalStop(self.width(), 0)
            else:
                grad.setStart(0, 0)
                grad.setFinalStop(w, 0)
        
        with XPainter(self) as painter:
            painter.fillRect(x, y, w, h, grad)
            
            # show the active action
            action = self.selectedAction()
            if action is not None and \
               not self.currentAction() and \
               not self._animating:
                for lbl in self.actionLabels():
                    if lbl.action() != action:
                        continue
                    
                    geom = lbl.geometry()
                    size = lbl.pixmapSize()
                    
                    if self.position() == self.Position.North:
                        x = geom.left()
                        y = 0
                        w = geom.width()
                        h = size.height() + geom.top() + 2
                    
                    elif self.position() == self.Position.East:
                        x = 0
                        y = geom.top()
                        w = size.width() + geom.left() + 2
                        h = geom.height()
                    
                    painter.setPen(QColor(140, 140, 40))
                    painter.setBrush(QColor(160, 160, 160))
                    painter.drawRect(x, y, w, h)
                    break