I honestly have a hard time following the argumentation here. Sure, there have been light grey horizontal lines, but with each section starting with a bigger font size, boldened and with minimum 1.5 times margin like between paragraphs, one could also argue the same about majority of websites out there where a smaller headline signifies a new section.

There is a minor issue though on closer inspection, that the font size wasn't at the aimed for 16px as intended, due to a generic element CSS rule that inherited all the way down into the OOUI structure of Special:Preferences.

In T208837#4751908, @Volker_E wrote:

There is a minor issue though on closer inspection, that the font size wasn't at the aimed for 16px as intended, due to a generic element CSS rule that inherited all the way down into the OOUI structure of Special:Preferences.

rMWe71c3439318e: Reset legend `font-size` in OOUI HTMLForms

I wonder if this would be enough to resolve this task?

Hopefully it would do, I would only like to suggest to unbold the only bold text, that is not a heading or a button: "Don't use images, external links and templates." in the signature description.

@Dvorapa That's similar to T194533 – it's a description provided by enwiki community. Your request would need to be raised there. Compare dewiki treatment:

I'm speking about cswiki. Per your response it seems it can be fixed somewhere in the MediaWiki namespace??

https://cs.wikipedia.org/wiki/MediaWiki:Tog-fancysig

(See also https://www.mediawiki.org/wiki/Help:System_message#Finding_messages_and_documentation about how to find the message names)

Wow, I didn't know about qqx feature, this is what I missed all the years!

Thank you