I went to the "My Profile" page but I don't see the option. I'm bad at internets.
Edit: Found it, and the dark theme is glorious. I have a bad sensitivity to bright lights and looking at a white screen can be painful at times, so this is perfect. It'd be cool if the TinyMCE editor has a dark theme as well so we can have that option when editing posts, too.
Ask and ye shall receive - I updated the skin for the editor, as well as the background in the editing area... ("dark mode" only)
Wow! I noticed the change a little bit ago and had to come back to find my post, as I wasn't sure if it was implemented because of my suggestion. That's really cool guys, thanks!