Very Simple Stack Boxes

This is a simple stacking box. This has 3 variations: 100x50x30 mm, 100x100x30 mm and 100x150x30 mm. You can only stack the same one onto each other, 2 small on one medium won’t fit for example. Of course, there are way better models than mine out there. But I made them to learn CAD software. Tell me what I could do better, or I you like them. I hope they are alright