“Dig deep within yourself, for there is a fountain of goodness ever ready to flow if you will keep digging. — Marcus Aurelius, Meditations, 7.59
What is negativity at its core? The absence of goodness.
Therefore, the best antidote to negative thoughts is to replace them with good thoughts.
The best antidote to negative emotions is to do things that make you feel good.
Don’t rely on the externals to experience goodness. Just find it in yourself.