Update code highlighting CSS
Update code highlighting CSS

Update the code highlighting theme to match better with the code
highlighting theme that we had before this commit's parent commit
generated a new Solarized Light theme based on Base16::Solarized
included in the Rouge gem.

Most changes were because the new Rouge gem creates different output for
the code compared to the older version. I think they improved some of
the detection of code segments to make it more detailed.

Some changes I left in were:

- YAML keys are now light blue. It helps differentiate between keys and
  values better.
- Numbers are now yellow-orange to differentiate between numbers and
  strings easier.
- Command line arguments in `sh` code blocks are now highlighted as
  orange.

appsignal/appsignal-docs