Improve W3C Web Content Accessibility Guidelines conformance by tweaking syntax highlighting colors?

[tim-seoss]

I noticed that the blog uses a code-block syntax highlighting colour scheme which is similar to the one that mdBook uses (i.e. the one used for the online versions of The Rust Book etc.).

mdBook merged a PR in Feb 2021 which increased the contrast of its default color scheme rust-lang/mdBook#1470

The current scheme used on the blog is actually somewhere between the old and new mdBook scheme (so that from a visual/contrast accessibility PoV it's slightly better than the old mdBook default scheme, falls short of the current mdBook default scheme).

I'd be happy to prepare a PR so that the blog could use the updated mdBook default colors if it's felt that this is likely to be merged. The mdBook PR (and the issue which it closes) contains some relevant discussion and references.