So cute! Custom cut to fit inside an Altoid's tin (well.. the blank ones we carry; an actual Altoid's tin is a hair wider than our blank ones).
Instructions: You have to kinda tilt it to slip it in. Then hook a finger inside and pull it forward to snug it up against the front. It stays put pretty well but I would add glue to it for a permanent assembly.
Set of 3 designs, as shown, cut from medium-weight chipboard.