AI-Driven Tic Tac Toe Game

I think the most difficult thing was integrating how I coded with an existing algorithm for minimax, it took quite some time. As for the areas I'm unsure of, well... I did not bother to implement any media queries since the website looked fine at all screen sizes. Maybe I was just being lazy but it did not really seem necessary. Additionally, I think my style of coding JS could use some work, in the end, the JS file was over 600 lines, which might be frowned upon by some individuals. How can I improve upon this?

With regards to how I did the HTML/CSS/JS, is there anything else I could improve upon? Thanks