Took me a bit of work, but I got controller support working. You'll still need your mouse to click on the yellow buttons, even if controller support is working, but while playing the game, you should be able to use a controller. Test on Windows with Xbox One controller. Let me know if it doesn't work on Linux.
My code after completing section 5 of the Unity class I'm taking on Udemy. Then I did a little extra to make it my own.