The staff of the forum I’m migrating doesn’t like a specific generated color variable (--tertiary-very-low) that makes this specific brownish color:
They would like to tweak it, and it seems I can’t really change it since there it’s generated AND is no parent-specific class for the dark mode.
However, I came across this information:
I don’t know if it’s valid, I couldn’t try it yet, too many things to do right now 
. But if it works, that will do. It would be even better, in fact.