Hallo Andreas,
after seeing the screenshot, I think we can be sure it wasn't the GTK theme after all... - sorry for the detour!
Something else: Could you recommend this book in german language?
Inkscape. Von Uwe Schöler. ISBN-13: 978-3446438651
- I'm sorry, I've never read the book. I only know that the author is a former German translator of the Inkscape program.
In our library, they had a copy of this one: ISBN-13: 978-3898645539 (and I don't remember too much about it - I've learnt a lot more from just playing around with the software, English online tutorials, and by getting involved with the community).
I don't know which Inkscape version the book by Uwe Schöler refers to, probably to 0.48.x. 0.91 doesn't differ a lot from 0.48 in the basic functionality, but many new features have been added. If you want to mainly learn the basics and standard techniques, it probably won't matter that it's not current (I never saw any book for 0.91 in German - or any other language).
If I needed a book, I'd take a look into Inkscape books in the library (or in a physical book store) first, and only then, if I really wanted to keep one, I'd buy it.
While you don't have a book yet, you can also start with a tutorial that follows one of my workshops ;) : http://vektorrascheln.de/posts/2015/Dec/inkscape-fuer-einsteiger-teil-i-grun... and http://vektorrascheln.de/posts/2015/Dec/inkscape-fuer-einsteiger-teil-ii-pra...
Or is there a better one in german?
- I honestly do not know :/
Kind regards, Maren