It's the second revision!

As the other people say, some version of the board has deeper bottom.

So, I lowered the card cubicle height by 5mm.

Also, I made some corners round.

Then, added the card holder step at 10mm height so that kids can take out the card easily by sliding fingers below the cards.

Original description below.

I just needed a case for keeping those cars.

The board acts as the lid.