You can always click on the scroll bars -- invisible doesn't mean they don't exist, they simply go out of the way when they're not needed (i.e. most of the time

You can always click on the scroll bars -- invisible doesn't mean they don't exist, they simply go out of the way when they're not needed (i.e. most of the time / when not scrolling). You can do that on iOS and Android as well, tap and hold on the scroll bar to quickly scroll through an entire document.