Add a white glow or background on the favicon.

[FabienTregan]

Hi,

The Rust favicon is black and transparent. On dark browser themes, it is not easy to see. Since rust book and github also have this particularity, it's hard to find the tab among the other ones.

Not really important, but if it is cheap to fix that would help :)

My tabs right now:

[CryZe]

GitHub seems to dynamically switch to a white icon for dark mode. Rust could probably do the same thing.

[FabienTregan]

Though great, the prefers-color-scheme media feature is not widely used.
I guess most people don't know they can turn windows into dark mode and lot of people use dark themes in their browsers instead of default theme with dark os setting. prefers-color-scheme only work with the later for me.

[frewsxcv]

Are all of these used?

• https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/static/favicon.ico
• https://github.com/rust-lang/www.rust-lang.org/blob/master/static/logos/favicon.ico
• https://github.com/rust-lang/www.rust-lang.org/blob/master/static/images/favicon.ico
• https://github.com/rust-lang/www.rust-lang.org/blob/master/static/images/favicon.svg
• https://github.com/rust-lang/www.rust-lang.org/blob/master/static/images/favicon-16x16.png
• https://github.com/rust-lang/www.rust-lang.org/blob/master/static/images/favicon-32x32.png