Yep, this is the way. You can test it works in Firefox dev tools by forcing the dark/light browser settings (you can set it to print too to test your print styl

Yep, this is the way. You can test it works in Firefox dev tools by forcing the dark/light browser settings (you can set it to print too to test your print stylesheet). It's a shame there isn't a standard high contrast setting, though. That seems more important than dark mode. Oh well.