Not going for any awards here, just a basic shelf (my son said it looks “modern” hence the name). Feel free to copy, remix or neither.

Simple 3 (or 4) piece design with tight tolerances for friction fit, no glue or unnecessary connectors. If you have a large enough printer (or need a small enough shelf), can just use “top shelf A.” If you're using a Mini, print A and B with zero top layers, and zero infill (at least the top 15mm) to join as shown.