Retro Commodore has published a high-resolution scan of the Amiga User Interface Style Guide.
“The purpose of this book is to describe how the user interface of a standard Amiga application should look and operate. It is intended to be read by current Amiga developers as well as developers who are considering writing and/or designing application software for the Amiga.”
It is a nice piece of history to see how the Amiga UI was generaly conceived and the reasons for certain elements be like they are.
As usual, Retro Commodore scans can be download for free, but expect them to be large files due to the high-quality.
Link: Retro Commodore