This design is easy to make.
Place sheeting over the light switch cover, tape it up in back (leaving open space behind the screw-holes and switch-panel), cut open the switch panel down the middle and fold-in the flaps, poke pinholes where the screws will penetrate, and screw the plate back into the wall.
Before taping up the back, you'll want to cut-off the corners of the sheet so the side flaps and top/bottom flaps can fold in without interfering with each other. Kinda like this:
You can use the switch cover itself as a physical guide as you fold-in the flaps.
I also made this by laser-cutting an acrylic sheet and adding a black vinyl backing:
