I used the Glowforge to make the center medallion as well. It’s two layers of black acrylic, with the lines that form the walls cut and glued on the bottom solid layer. Then filled in with an iridescent paint then domed with two-part epoxy resin. The middle of the lid is engraved to make a slot for this piece.
I found I got the best results by using hardwood (Proofgrade basswood for this one) rather than plywood, so I could sand off the finish so it would bend easier. I didn’t have any nonPG hardwood that did not have finish, or I would have tried that.
The boxes that you made are stunning. I especially like the way you got your curved sides. Even the artistic way you made the tabs gives another level of beauty. Did you get the curved edge shape on your 2-part epoxy through just the surface tension?