Diagnosis
Moisture and toothpaste residue have accumulated in the drainage holes on the bottom of the glass charger base, leading to visible grime.
How to Fix It
Use a pin or unbent paperclip. Unplug the charger. Turn it upside down. Gently insert a pin into each of the four small drainage holes to dislodge the compacted debris. Follow by wiping the entire base with a cloth dampened with rubbing alcohol (not water) to disinfect and dissolve residue.
If That Didn't Work
For severe buildup, use compressed air. With the base unplugged and upside down, use a can of compressed air (like for keyboards) to blow forcefully through the holes from the bottom side.
Heads Up
Never submerge the glass charger base in water or run it under the tap. The electronics inside are not waterproof. Only clean when completely unplugged.