@nicod_ @aral Yeah, there's something weird here on Firefox 78 on Linux. It looks like the "background-color: #eee" in the dark mode block is getting applied without then being inverted. If you change it to #111 it looks great, and is probably the intended effect.
I wonder if the background color on the html element is handled specially in Firefox, and escapes the filter. If you change that rule to target body, it works as desired (but you know, narrower).
@aral @varx @email@example.com potentially relevant: https://stackoverflow.com/questions/61246462/css-filterinvert-not-working-with-background-color/61265706#61265706
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