If the admins decide to actually spend some time and install a theme then I suggest to install
wGame
https://custom.simplemachines.org/themes/index.php?lemma=2943It has all three features requested so far it has light and dark colors and from a very quick test it seems to handle smaller sizes as good as the default one but I do not know if I would call it "responsive".
I don't think they will do. All of the SMF based forum I have seen use the default theme.
I understand I made the original recommendation.
You could just use Dark Reader extension like me
It does not work with firefox it crashes in this forums and shows the message that an addin slows the browser down...
Now if everyone that cares to see a theme install made a recommendation of his/hers favorite theme and enough themes are proposed, then we can start a small voting process on what you would like to see included.
Keep in mind that I do not think the admins will even consider installing themes at this point so this is more of a "lets have some fun selecting a theme".