@ClemensPitschke It depends a bit what you want to achieve - there are usecases for which I'm happy to provide more guidance (as a video e.g.), however for instance the possibility to do css customizations with this is something that, for me personally, is a coincidental outcome, not a thing I want(ed) to actively encourage everyone to do.

I know that some people feel about this exactly the opposite way, and I don't think there's a wrong or right here (their point is just as valid), but my approach right now is to try to establish a clear division between customization that is safe, fun and productive for absolutely everyone - (almost) no learning curve, intuitive controls, doesn't break anything, most or every configuration is functionally and aesthetically sensible - and such customization that allows unlimited flexibility, but has equally unlimited potential for being broken, dysfunctional, complicated, annoying, unusable, unproductive, etc. when people don't know what they're getting themselves into or things just go awry.

Custom CSS falls in the latter category, and I'm not per se happy with this wild potential being unwittingly unleashed on everyone through site_metadata now, but I considered other usecases of site_metadata (e.g. including analytics) too important to justify an artificial limitation here.