HABPanel: Where are the files?

Hi guys
I try to configure HABPanel, my first panel, and cannot find the location of HABPanel.conf and where to store css files.
I search openhab docu and the internet, but all I got were some hints about openhab2 and filestorage, but nothing fits.
I use Openhab3 on raspberry pi4 raspberryOS (bullseye) installed the apt packages
Maybe I’m too dumb but can anybody explain where are the file locations described or gimme an overview ?


But I had to use ‘locate’ to get the location:
…and where to store the “additional_stylesheet_url” files ?

It’s all in the docs:

I only know of inline css.