Can't scroll even though content extends out of the window, any ideas?

Hello, I am building a simple Node JS app: https://glitch.com/edit/#!/pbs-mining

Even though the main canvas extends out of visible area, scrolling is impossible. I tried to force scrollbars using overflow: scroll; but it doesn’t work.

In order to show the canvas, you need to enter any number in the login bar and press button A.

Thank you for any ideas.