Support dark color schemes

[cassidyjames]

With browsers across macOS, Android, Windows, and soon iOS and GNOME Web supporting the prefers-color-scheme media query, we should support it for our site as well. This involves a few tasks:

• Support the media query itself with a specific dark color scheme
• Check images and ensure major ones (i.e. on the front page) don't have hardcoded white backgrounds—instead, we should use transparent PNGs
• Test at least on macOS Safari and Chrome Canary for Android

More info: https://webkit.org/blog/8840/dark-mode-support-in-webkit/

[AdityaSPatil]

Should I work on this? @cassidyjames

[cassidyjames]

@AdityaFRC you're welcome to! See #2193, and you are welcome to continue the work from there.

[elsiehupp]

Hi! Has there been any progress on this in the past two years or so? The fact that Elementary OS 6 Odin natively supports system-wide Dark Mode seems like a good impetus here...

[elsiehupp]

Dark Mode CSS is kind of a focus area for me right now personally, so I'd be happy to help.

[lewisgoddard]

I think #2193 is as far as we got, #2284 also exists but has a lot of conflicts.