Drill a hole in the side or the back of your frame to let the power cord through. I used a rotary tool for this.
Use hot glue to secure your power cord, Feather, and LED matrix in place inside your frame. I found it worked well to glue along the top edge of the matrix and fix that to the top of the frame, since it doesn't sit flat inside the box.
To attach the resin piece to the frame, I used four rare earth magnets and four spare nuts from a jar in my shop. I used E6800 glue to secure the bolts to the inside of the frame, about 1/4" down from the top.
Measure between the bolts and place the magnets on the back of the acrylic where they'll meet up and fit snugly. Use a generous amount of glue and let it dry completely - these magnets are STRONG and will overrule weaker glue.
If you are adding the inline on/off switch, plug it into the Feather and the power cord and mount it someplace convenient on the edge of your box - you may need to drill another hole depending on your setup.
Hang it on a wall with picture hanging hardware or set it on your desk like a picture frame. Enjoy your beautiful, magical, bioluminescent ocean.