Buttons are in different placements in different resolution

Question

So I have been creating a tic-tac-toe game, and right now it is a 2-player game. I got the main gameplay done. The tic-tac-toe buttons on your screen might not be a 3x3, because the resolution can affect that, I don't know how to fix that.
My Code: https://code.sololearn.com/WhGj559thn65/#js

Answer 1

After the third and the sixth buttons, place <br/> to have a line break between each three.