Summary

Printed this swanlake lightbox from zorroronoa for my daughter (https://www.thingiverse.com/thing:6241043), I loved it, my daughter loved it.
Decided I wanted to make my own lightbox design to work on my tinkercad skills, kept the same size cards as the original as they are awesome and as it can be a while before I make my own (if ever :)).
I added some more slots and space for an extra LED strip.
Went with a 4-5-4 slot arrangement with an open back so it can be made see trough.

Didn't print this final version of the top part myself yet, made some small changes to hopefully make the bottom fit more easily and also some space to hide the wiring/led strip so it doesn't come in the way of the cards as much.

Only the bottom part needs some supports.
The 2 bars should stay in place well enough once you stick a LED strip on it and should give enough flex to keep the bottom in place, if not just use the holes in the bottom to put a few screws in.

As lightsource I used a 2m COB RGB LED strip (WS2812B), but 1.5m should be enough. I didnt cut the strip, just lopped it trough the other side.