Ooopsies happen to anyone, and dropping textures on a many-faces object is clearly a major risk for oops.
If you accidentially dropped your texture to a face of the TDS Book Creator thats not intended for those kind of ooops there’s a simple way to restore the original textures.
Open up the menu, click the “Fix textures” button and there you are again, cleaned up buttons and background textures.
Does that mean you can’t customize the background or button textures? No, you can still customize them. But after customizing the look of the Book Creator, please reset the scripts inside once, so the’ll store that state as expected preset!