Right, so there is such a thing as going too far… this should at least be a configurable option so that folks who want web sites to adapt to their system light/dark mode settings can have that.
There’s a line between protecting people and being paternalistic. And I can’t believe I’m the one having to say this but privacy isn’t the only concern when designing (e.g., in this case you might be overriding someone’s accessibility preferences).

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