Some small stackable shelving, created in Tinkercad.

Printer: Creality Ender 2 Pro

Filament: Sunlu PLA Grass Green

Infill: I used 25%, but given the small size, I don't think it matters.

Supports: for the base of the first section

Connection:  I found I had to carefully drill out the holes for the guide pegs, so XY hole compensation is a good idea (I didn't use it, hence my drilling).  I also applied a bit of CA glue to the guide pegs before putting it together.