Dark theme (again)

[VitalSkib]

Hi.
Is it possible to somehow add a dark theme to your extension?
Something simple (see the image) would do..
One switch in the Option to load the style_dark.css file, instead of style.css, which is default.
Or could you tell me if there is a way how can I override these two files (style.css and on-off-switch.css)?
I mean, it is very easy with usual web sites, but I couldn't figure out how to do it with extensions styles.
Thanks in advance.

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