paint method
Draw itself and its children, according to the calculated
box.offset
Implementation
@override
void paint(Context context) {
super.paint(context);
context.canvas
..setStrokeColor(color)
..moveTo(box!.x, box!.y)
..lineTo(box!.right, box!.top)
..moveTo(box!.x, box!.top)
..lineTo(box!.right, box!.y)
..drawBox(box!)
..setLineWidth(strokeWidth)
..strokePath();
}