Four years ago when the user @etcSudoers created this thread the ability to customise Joplin using CSS was quite a new and popular thing. The use of custom CSS is unsupported so user-to-user support was all that could be expected. This thread was never going to be an "official" repository of all CSS knowledge, but just a quick way to share useful info and discoveries. It just grew all by itself. When someone was experimenting and searched something like span.cm-variable-2, they got this thread in their results. Others referenced posts within it, and so it continued to grow. I agree that you cannot really read this thread from beginning to end and it sort of became a "CSS chat-space". It is not as popular as it was and up until your post had not been updated for a month.
A while back an attempt was made to make a more organised "repository" and this forum "wiki" page was created. In my opinion the Discourse wiki function is not that brilliant and you almost need to know the page exists to be able to find it, but that is what we have.
So...
This is just a thread that Joplin users have created and updated by themselves as they see fit, just like most of the 1000's of other threads on this forum.
(My emphasis)
For some reason you seem to assume that Laurent / Joplin has been providing this post as a source of best practice / knowledge for this unsupported feature, which is not true. I may be wrong and "you" may just be pointing at Joplin users but, regardless, it's just another forum thread.
It would be fantastic if there was a properly structured wiki containing a comprehensive user manual / documentation for both users and developers but for such a small group of volunteers I doubt that there is enough time to create and adequately maintain one. Especially considering the pace of change. However I doubt that CSS customisation, being an unsupported feature, would be included in any official wiki anyway.