open fun inset(dx: Double, dy: Double): Unit
Inset the rectangle by (dx,dy). If dx is positive, then the sides are moved inwards, making the rectangle narrower. If dx is negative, then the sides are moved outwards, making the rectangle wider. The same holds true for dy and the top and bottom.
dx - Double: The amount to add(subtract) from the rectangle's left(right)
dy - Double: The amount to add(subtract) from the rectangle's top(bottom)