Well the title doesn't lie, it sure is a nice and simple Tic Tac Toe!
The UI and design of it is very nice though! Feels like it could be thrown on a phone right now and it would fit right in with any other mobile game. I am curious how the opponent picks the spot it wants to play in, as it seemed to pass up obvious blocks a lot of the time. But it's also no fun playing against a perfect AI, especially for Tic Tac Toe.
Great job overall! You finished and released a project, which is one of the hardest steps to take! Well done!