I turned my themes into a more easily customizable theme. From the stylus extension button, you can change the background color, text, and accent color using a color picker.
It comes with 20 pre-made themes as well, some are shown in the image.
Download here (userstyles.world)
Or here (github)
(userstyles.world is having some problems with downloads right now, if you get an API error try the github link.)