How can I create Transparent Holes in my project?

I am making a spin-off, off of the challenge "Hoppy Beaver Extreme" and want to make a custom win screen. I want to make Hopper hold a few rings in his paw. Is there something in the code that can make an object (or part of an object) see through to see other objects behind it? I tried make the color for the ellipse, that makes the hole, transparent but then all I see is just the brown of the circle that makes the ring.

The project: https://www.khanacademy.org/computer-programming/spin-off-of-project-hoppy-beaver-extreme/6327002772045824