Stylus should rotate dark styles with normal styles based on geoposition and timezone by default. Similar to the https://addons.mozilla.org/en-US/firefox/addon/automatic-dark https://github.com/skhzhang/time-based-themes

I use this to write CSS to fix broken sites and remove overintrusive ads that escape ad blocker. Actually works, unlike new Stylish. Interface a bit clunky, hence 4 stars.

does not work on loaded local pdf files. stylus says "Firefox forbids access to the site, In Firefox 60 and newer you need to remove this domain from extensions.webextensions.restrictedDomains in about:config."

however the local files are not in any domain

Love this addon. Only issue is the editor window does not remember which monitor to open on in a multi-monitor setup nor the last used window size; in my case, maximized on monitor #2.

Very cool. The editor has live preview, syntax autocomplete, colour pickers, and different colour themes to choose from.
Can even use it to customise it's own UI, nice!