I'm guessing he replaced every .png file with a blank image
I think you replaced all the detailed .pngs with blanks.
I didn't. I don't know how, although I doubt it's very hard. I went into fullscreen via key command (CMD+ENTER) and it didn't work, the window just disappeared. I was confused and though, that maybe if I tried the command again it would bring the window back, and it did!
With one exception...