Zooming in and out of the rulebook causes a zoom out in the game
When opening the rulebook and scrolling through it, it scrolls the canvas with the game behind it. I don't have access to the code so I can't tell what methods you used for the rulebook popup, but from my understanding of css, it could be fixed using a modal and adding overflow properties, however I'm not sure it is that easy or is related to the popup itself and not the canvas renderer.