It is not yet possible to configure the instance in Backtivisda. You need to modify the files directly in the Gitlab project.
Various parameters are defined in the local/localconfiguration.json file, in particular: the name of the instance, its url, the languages available, etc.
Modify the local/buefy.scss file and in particular :
--primary-color--secondary-color$title-font: to specify the font for all titlesThe favicon is the little icon next to the name of the site in your browser's tab bar.
All you need to do is change the favicon.ico file to one with the same name.
A 64x64px favicon is fine.