I designed these little shelves to fill the corner in my bathroom and free up some counter space.  They have slots in the bottom so you can slide them over four screws.  The slots make them easier to install and remove.  But if you put too much weight on the edge they may flip down.  The shelves are relatively stiff, and should be strong enough for most things that fit on that small of a shelf.  One version of the shelves is 100mm on each side.  The other one is 100mm x 120mm so it sticks out past my mirror.  If someone wants a version with holes instead of slots, I can do that easily.