Line up the bare panel so it is sitting squarely on top of the cube's sides. The screw holes are symmetrical around the perimeter, so at this point the orientation doesn't matter. Attaching the top and bottom panels will be one of the last steps after all wiring is complete.
Take the small phillips screws and hold it steady while screwing them in around the perimeter. You'll need to drill pilot holes so screw just enough to make a mark as a guide. I used a 1.51mm bit.
The drilling will create a lot of plastic debris, so it is best to do this before mounting more components inside.
Repeat this for the other side. Do not attach the panels yet.
Make sure the holes line up and move on to the next step!