Support for dark mode

[codewithtyler]

As a developer we typically look at screens most of our day. As a result the bright screen can sometimes cause headaches. It would be nice if there was a toggle button at the top of the page perhaps near the Contact Me button that lets you toggle between dark mode and light mode. You could even have it where when you toggle the button some JavaScript will save the current mode in local storage so that the next time the viewer visits the site it remembers what you set it to. This could even be an extension of the color variants support you have now where you can separate color variants for light mode and dark mode.

[ishanvyas22]

Really love to see this feature in this theme. @wkocjan Since we already have color variant for dark-blue which I suppose can act as an dark mode, is there any easy way around to quickly switch classic color variant to dark-blue until we have proper official support for dark mode?

[alcrene]

In case someone is interested, I implemented this in my fork: I add a dark-theme option, which accepts exactly the same arguments as theme.
I'd be happy to merge this back upstream.