Inspired by this video: https://www.youtube.com/watch?v=Nz8ssH7LiB0

Everything goes in the square hole.

Important:

• Print the top part with 1-2 layers of one color then solid black for the rest.

• Print the bottom part in black.

• Use a bead of cyanoacrylate adhesive (e.g. super glue) around the inner rim to glue to the top to the bottom.

If you don't print it in black, it'll be visually obvious that the parts won't fit. If you don't make the top a different color, it'll be easier to focus on the black underneath.