Is it possible to adapt the CSS-settings for text?

As first Thank you for this fantastic tool. I’m using Xibo now for many years and very glad to install the new version.
I did not find an answer about the possibility to edit basic CSS.
Because my basic template uses a dark blue background image, I would like to adapt the h1, h2, p etc. syntax to lighter colours.

Where can I find the CSS file to adapt it?

Kind regards,
Guenter