We [render rust by example with the latest mdbook](https://github.com/rust-lang/rust-by-example/blob/master/.travis.yml#L10), and today, something is messed up. Look at the code blocks here: https://rustbyexample.com/flow_control/match.html They're dark black, and impossible to read. I haven't dug into the details yet, but maybe someone else knows?