Oh, that isn't what I meant. The clear molded plastic sheet is molded because it has the shape of a keyboard with keys. The keys will move and spring up as usual, in fact many standard keyboards and keypads are made like this (but with black plastic and painted symbols).

It might need to be made of two different materials, one rubber sheet between the keys to make the keys spring back well and one clear plastic to allow you to see the screen through the keys, but it might even be possible to make in a single material that is not only transparent but also sufficiently springy when thin and sufficiently hard when thick; I don't know enough about the material options available, but I have gotten the impression that there are very many to choose from.