Summary

The tea-warmer is printed in neutral (transparent) PLA. A slow fade led which is connected to a 4.5 volt battery holder through a resistor of 56 Ohms is pushed into the sphere. The sphere is pushed into the tea-warmer, while the wires are guided to the opening at the side.
The battery holder is hidden in a match box.
If you want to switch it off, just remove one battery from the holder and put it alongside in the matchbox.
https://youtu.be/e672pToTUSY