Where would the buttons go best?

I made a browser app, and have gotten some positive feedback, and someone asked if I could put buttons on it.

It is located here: https://freezephoenix.github.io/FireSnake/3D.html

Background: You use the right and left arrow keys to control the snake. However, there are no arrow keys on mobile, I would like to add buttons to the game. I was wondering where they would go best.