First of all, a big thank you to TechDino for his beautiful work and for making the 21 available to me (to all).

I made some modifications:

1. Instead of the LEDs used, I used a 1m - 5V Cob LED strip.
2. Since I had a round on/off switch I used this.
3. I didn't want to operate the lamp with a battery but rather permanently and so I installed a round USB-C socket.
4. I had to adjust the frame to close the rectangular hole for the designated switch on the left side.
5. Two holes had to be created on the right side for the switch and the USB-C socket.
6. I also created a hole in the lid to make it easier to open the lid again.

All items are from Aliexpress:

1. Cob LED, white, 320LEDs 5mm 5V, 1m
2. USB-C Buchse mit LED rund zum Einbau inkl. Kabel und PH 2.0 Buchse in schwarz
3. Runder Kippschalter in schwarz
4. PH 2.0 Stecker mit Kabel

The wiring is relatively simple

1. The red wire from the LED strip is soldered to one side of the switch.
2. The other side of the switch is connected to the red cable of the USB-C socket (a PH 2.0 cable was used here because I had it and the USB-C socket has the corresponding counterpart). You can also cut off the PH 2.0 plug on the USB-C socket and then solder the red cable directly to the toggle switch.
3. Now the black cable from the USB-C socket and the black cable from the LED strip are connected.
4. All soldering points were covered with shrink tubing.