This isn't even a government design standard (or government website for that matter). If looking into the impress you will find that it is run by a Verein that's promoting tourism. To quote:

> Promotion of Austria as a holiday destination.

There is a corporate design guide available [0] but from what I can tell it's more of a guide for "everything" not just websites.

[0]: https://www.bundeskanzleramt.gv.at/service/corporate-design....