I recently decided to dig in and try to squash this task, originally intending simply to document the allowed properties, but over the course of the work it ended up touching nearly every part of the Help page. The largest part of the new material can be found in the collapsible box at Help:TemplateStyles § Allowed CSS properties and rules on the MediaWiki wiki. Obviously I fully expect that I didn't get everything 100% correct and so I'll gladly revise any mistakes that are spotted; I went into this never having looked at the codebase and possessing an intermediate level (at most) of experience with front-end work. Perhaps with a bit of grace that will have worked to my advantage and helped me find a middle ground between sounding pedantically indifferent or patronizingly insulting. There's still a bit more I want to expand/edit/polish and I'll probably be able to knock that out towards the end of this coming week.

So is this still ongoing? The site's been down again for approaching a full month again by my reckoning.

In T231400#5485842, @Isarra wrote:

What exactly is geohack, that's adding these coordinates in the first place? Is this an extension, template, what?