Box for word learning cards

I've made a box to store 4 stacks of cards for learning words but it can surely be used to learn other things like math formulas or coding commands.

The idea is to write a word to learn on one side and explanation on the other side.
Make as much as you like, shuffle them and try to guess each one by one.

Cards are made from thicker A4 paper, cut into 3x5 cm rectangles.