How do I close the investor encyclopedia?

[DiseasedProject]

I'm either stupid or blind, but I can't for the life of me figure out how to close the investor encyclopedia. I've played the tutorial many times and it says something about a button, but there's no visual clue to any button anywhere. The encyclopedia takes a lot of room on the screen and I just want to know, how to close it. I've tried clicking every other pixel but the one that does the desired action, apparently.