Source Code Pro is the font they're using.
https://github.com/adobe/Source-Code-Pro
https://github.com/adobe/Source-Code-Pro/downloads
Syntax highlighting is done via Code Mirror
All extensions available are listed here.
Question
Does anyone know? Also what syntax highlighter is is using? Prettify etc?
Solution
Source Code Pro is the font they're using.
https://github.com/adobe/Source-Code-Pro
https://github.com/adobe/Source-Code-Pro/downloads
Syntax highlighting is done via Code Mirror
All extensions available are listed here.