Hi @vrm
Thanks for letting us know your user experience. According to your case description, I do understand how frustrated you are now.
When I received the case, I searched a lot of documents did a lot of researches. And I feel regretful to inform you that it turns out to be a by-design one.
I do some test:
Here is list Name:
F12 to modify CSS style:
I try to use the SPFX extension to modify the style of such elements that appear in CSS selectors.
Unfortunately, it cannot be implemented, some unexpected exceptions have occurred, and I have no way to fix them
If I find a solution, I will tell you, but the way you want can be achieved through SPFX, but there are often some unexpected situations
Here is link for your reference:
https://learn.microsoft.com/en-us/sharepoint/dev/spfx/sharepoint-framework-overview
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Best Regards
Cheng Feng