'Draw the background rectangle using the current style primitive color.
:param rect: The fold zone rect to draw
:param painter: The widget\'s painter.'

def _draw_rect(self, rect, painter):

    c = self.editor.sideareas_color
    grad = QLinearGradient(rect.topLeft(), rect.topRight())
    if (sys.platform == 'darwin'):
        grad.setColorAt(0, c.lighter(100))
        grad.setColorAt(1, c.lighter(110))
        outline = c.darker(110)
    else:
        grad.setColorAt(0, c.lighter(110))
        grad.setColorAt(1, c.lighter(130))
        outline = c.darker(100)
    painter.fillRect(rect, grad)
    painter.setPen(QPen(outline))
    painter.drawLine((rect.topLeft() + QPointF(1, 0)), (rect.topRight() - QPointF(1, 0)))
    painter.drawLine((rect.bottomLeft() + QPointF(1, 0)), (rect.bottomRight() - QPointF(1, 0)))
    painter.drawLine((rect.topRight() + QPointF(0, 1)), (rect.bottomRight() - QPointF(0, 1)))
    painter.drawLine((rect.topLeft() + QPointF(0, 1)), (rect.bottomLeft() - QPointF(0, 1)))
