Designing took about 2 months of hard work and lots of testing had to be done just to get it to work properly.
The "seesaw" in the center is the main mechanical part that rotates with the movement of the buttons. When the top is put on, it locks the buttons in so they don't move too much and fall out.

3D Printing Settings

0.2 mm resolution
PLA filament
70 mm/s
10% infill
No supports
No Raft or Brim

To assemble:
1. Place buttons in base slots with the stopper facing inwards
2. Slide the seesaw onto the pillar in the center of the base
3. Glue the top on to prevent parts from falling out