Directly to you from Twitter:
Happy Pokémon Day! Celebrate all things Pokémon with festive Pikachu wearing party hats available in the wild from February 26 to February 28. pic.twitter.com/pwRau4YFzw— Pokémon GO (@PokemonGoApp) February 26, 2018
…Wanna play? Buy a 3DS.
That being said, click on Pokémon Go for everything you need to know about the game. 😀