Measure out how many neopixels you'll want on each side against your pattern. Carefully cut through the solder pads between pixels and slip the silicone sleeve off.
Tin the pads on both sides of the pixels at the "in" end. Cut two 6-8" red, white, and black wires. Solder the red and black to the front of the neopixel strip to + and -, and solder the white wire to the back of the neopixel strip (double checking again that you're on the "in" end).
Temporarily twist the matching wires from each strip together and twist them into the Circuit Playground's VBAT, 12 and G pins. Turn on the Circuit Playground and be sure all the lights come on and work. This is a great time to find any bad or broken pixels!
Cut two more 6" red, black and black wires, and 2 6" yellow wires
Solder both red and black wires into the + and - pads of the first pixel. Solder one yellow wire to both the in and out pads.
Solder the second pixel "in" to the wire coming "out" of the first pixel, and solder the red and black wires to this pixel's + and - pads.
Temporarily twist-test these with your Circuit Playground as well to be sure they're working.
We will wait a bit to solder the lights to the Circuit Playground; first, let's prep our acrylic and get our layout right so we can be sure we have the wires the right length.