Since it's not immediately obvious and in case anyone is searching for it, the theme switcher is the icon in the header next to the search icon. It's either a moon or a sun.

I am a fan of dark mode. However, when I am reading articles I think white would be great when I am not reading plain text. I think so because, I ,may be most people, are tend to understand more from pictures than plain text and since Hashnode is a place with text and images I think dark mode would kill the way images look. So, I don't personally prefer dark mode for articles. :) However, that would be a welcome addition when I am just reading plain text.

Great work guys. Cheers :)