Calendar Core - Needs any special theme?

sure, this is easy for me as noob “gg”
buschitut.eu is main website with tab “g2g”.
sure all apps runs anyway extern or on subdomains as discourse.buschitut.eu
in the next step i like to add a footer for category’s & topics, which do content an “accordion” to run for this category/topic_name the same name forgejo and matrix spaces, i THINK that will be an “handy” way to have “all on one place”…