userstyles without Stylish

[bada.b...@gmail.com]

I don't understand the power of the :style command and the like. Is there a way to use a userstyle like e.g. https://userstyles.org/styles/23516/midnight-surfing-global-dark-style without stylish in Pentadactyl?
I'd like to toggle the style with a keymap to darken the entire internet. For now I just saved the style in ~/.pentadactyl/CSS/*. Sadly I don't have a clue about CSS and the like...