This is a simple enclosure for an 16x16 neopixel matrix. You can search amazon, ebay, or other sites for "neopixel 16x16 matrix" to find them at inexpensive prices. For more information see the guides on the Adafruit website.
The top is intended to be a diffuser, I find "clear" PLA or PETG works well if printed with 100% infill.
There are two tops provided, a 2mm version and a 5mm version depending on how much diffusion you want. To make the diffuser work, you can try different infils but I liked 3-4 top and bottom layers and a "Hilbert Curve" infill.
This version is a bit trickier to assemble compared to the 8x8 matrix, because I didn't the solder contacts of the matrix (or any part of it) exposed out the back. Either: 1) solder bare wires without a connector to the matrix, and then thread them out the hole in the side while placing the matrix in the enclosure and gently pulling on the wires at the same time, or 2) thread the wires from a connector through the hole in the side, then solder them to the matrix, and then place matrix in the enclosure while gently pulling on the connector at the same time. The idea is to keep the wires taut so they fall into the slot at the bottom of the enclosure.
Note: The 2mm diffuser is the one I'd recommend as it seems to provide the best visual results. For this I recommend using all 9 push pins to secure it. The 5mm is generally more stable but less bright, it only requires 4 push pins in the corner.
video demonstration: https://www.youtube.com/watch?v=nrhs21as4Ao