A website that is bright by default isn't accessible to some people with photophobia (which has a myriad of causes). https://en.wikipedia.org/wiki/Photophobia But some people have precisely the opposite sort of issue.
I maintain that no stylesheet can be accessible to everybody. If any accessibility-assessment tool says otherwise, that reflects a failure of that tool to consider some classes of visual impairment.
i can't tell you how much i struggle on a daily basis with websites who have passed these "standards". i don't even have anything serious. i just can't read small text well.
so my browser zoom is 150% by default which i adjust if it's too big. that all i did!
my setting has broken major sites on a daily basis. that tool that another poster linked is broken on my side! that's the tool that's telling people they are not following standards...
I maintain that no stylesheet can be accessible to everybody. If any accessibility-assessment tool says otherwise, that reflects a failure of that tool to consider some classes of visual impairment.