How to make a rectangle out of a polygon collider?

Question

Unity

There is a condition in Cinemachine - you need to define the boundaries of the polygon with a collider (I didn’t really understand how to work with it with a composite collider), although a box collider would be much more convenient (this is a screen, the screen always has 4 sides), so is it possible somehow set up a polygon collider to edit like a box collider?

Yes, of course, you can visually customize it so that it looks like a rectangle or a square, but it looks like ....
And is it possible to see these borders while you are working on other objects?