A complete waste of time trying to bring back the system theme that Firefox screwed up.
If you want to to something useful allow us to configure the _existing_ theme then not a useless preset

Only wanted to change active tab colour in dark theme (actually "System theme, following operating system" which is set to dark mode).
Couldn't figure out what was meant by various items I can change.
It changed more than it indicated.
Neither Undo nor Revert actually work.
Opened issue in GitHub.
Disabled add-on until it can do this 1 simple and commonly wanted tweak.
Investigating userchrome.css

Great addition! But there is also a minus - there is no translation 😢

All I wanted to do was change the color of the active tab so I can see it more easily. The second I clicked on that one new color, it changed EVERYTHING, and it looked horrible. I can't remove this add-on fast enough.

非常cool的功能，太喜欢了！

Great add-on. Recently I've started saving my themes the problem I have is when I restart my browser all my saved themes are gone, even more weirder is how the last changes I made are still there but do not show up as saved.

Everyone should have this. Allows so much more then the generic white/black/grey/red themes I otherwise see on other browsers.