I have a box of tissues in every room of my house. I made these to dress them up a bit and they also keep the boxes from lifting off the table when you pull tissues out. The bottoms of the covers are not meant to touch the surface on which the tissue box sits. This keeps them from scraping the surface and doesn't let the box of tissues flop around inside like the store bought ones. They fit most of the cube style boxes I've tried. There are two styles, one with chamfered edges and one with filleted edges.

Update 2-22-20: I have added another design with thicker walls and more rounded edges.