Computer chair cushion

I made this simple chair cushion for my son's computer chair. the padding in the seat of the chair had moved around to the edges making the main seat quite uncomfortable. My son took me to get the foam and he chose some 5" foam so plenty of cushiness this time. I covered it with black Duck Canvas and I put a concealed zipper in that went half way around the sides and all across the back so it would be really easy to take the cover off to wash. To be fair when I gave it to him it wasn't covered in dog hair! Luckily that vacuums off easy enough, but good thing the cover can be removed. Maybe I should make a spare cover.