Joystick seems to be working well. Gently pressing one side of the button seems to dim the fibers slowly as intended! Fibers are illuminated by a 3 mm red LED. The LED is powered by 2 AAA batteries through a resistor. Here is how they look in the camera:
First impression is that the button(s) can be pressed too deep on one side blocking the light on all fibers. I will make the lid thicker to prevent this. Also, I think I am going to turn the "X" in the joystick body 45 degrees to make it easier to read the joystick... I though having 2 fibers dim when one corner is pressed would be better but it might be the opposite.