Dark Mode Support

[mgifford]

I realize it hasn't quite come to the Windows world, but would love to have support for Dark mode built into Aurora. Would love to see this tie into WET as well.

There are going to be a bunch of related issues around assets:
wet-boew/wet-boew#8691

[RobJohnston]

Windows 10 provides a dark theme, and a website can determine the user's preference and present itself with it's own dark theme, as in the example provided from this Stack Overflow answer: https://stackoverflow.com/a/52986538/4930982

See also "Detecting the desire for light or dark color schemes: the prefers-color-scheme feature", at https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme

Edit: Instructions to set the new dark mode in Windows (requires a recent update that not everyone would have yet)
https://www.cnet.com/how-to/windows-10-dark-mode-is-here-turn-it-on-now/