Make variables translatable + minor css

[ghost]

1. Corrected elements in markdown and yaml files to make certain elements (mostly titles) pulled out for translation (add @).
2. Fix CSS so that red highlighting doesn't display for syntax highlighting (like we had before in PR 286)

[leeee]

Looks good, thank you!

[ghost]

@leeee - thanks! Should I extract translations as well? Actually when I did (locally), I got a lot more in the messages.pot file (a lot of translated text). I'm wondering if the translated yaml files were needed (for example, overview@ar.yaml), that is, the translation text could be addressed in the language's po file; or at least remove the @ in the translated files so the text isn't extracted.