Wanting to tweak the colors in the dark dashboard theme

Can anyone tell me where to find the color definitions for the elements in the dark theme for the dashboard? Thanks.

Start with dark theme then change to custom theme and the other fields will appear.

Yes, I saw that, but the custom theme is not populated with the same settings as either of the predefined themes. I have no idea where those settings came from, but I would like to be able to enter the dark theme settings and make a few changes