Syntax of this file is based on MapCSS file format, with some unique features and some limitations.
There is no documentation about our branch of MapCSS (TBD), just read the comments inside the style and look for similar cases as examples.
How to use
To force application to use your map style just put *.mapcss files to File Sharing folder of the Galileo and relaunch the app. Only map style is loaded and custom resources is not supported yet.
We're open to pull requests. Don't hesitate.