Hello PatK,
Unfortunately, your query is far too general to provide a meaningful answer.
Is it about the live page or the edit mode? If the former, are static pages being used or dynamic pages (e.g. a PWA)? If the latter, is it about changing the appearance of elements generated by FirstSpirit (in simple terms, this is everything that looks different in edit mode than in live mode)?
If it is about changes to the CSS/JSS that is used on the live page, this is explicitly defined within the [page-]template and can be changed accordingly. Identify the appropiate code within the template (should be a $CMS_REF(media:"...")$ Tag) and, with pressed CTRL, left click it. Than you should see the media with the appropriate code. ATTENTION: If you change anything here, it will be changed on all pages, which use this media!
With the elements generated by FirstSpirit, it depends on what is to be changed and how.
Note: If this answer helps you, it would be a good idea to attend a training to learn these basics 🙂
best regards
Holger
