Well done @joebuhlig - awesome setup (I assume of the free open source version). Just to hit perfection, on sign up, when I clicked the confirmation email - the confirmation screen isn’t using the chosen theme.
Which is, of course, no contest, dark mode.
You may want to go into your user settings (icon in the top right, settings cog, interface), and set the default theme for all devices. I know on iOS the confirmation opens in the browser rather than the app which is seen as a different session - so uses the default theme from your profile 
This was all on the PC, so it should have been in dark mode, but I have also set the preference so signing in on iOS gave the lovely darkness I crave.
If memory serves, the activation page ignores user-selected themes due to potential security concerns. That page is one of the most important in the entire package so it’s best if developers leave it alone. At least, that’s my understanding.