Install other libraries or Ruby gems in Koala - oklai/koala GitHub Wiki
If you haven’t already installed Sass and Compass:
gem install sass
gem install compass
Then install the library:
e.g. gem install zen-grids
For Compass project, your project should have a config.rb file. Add the require line to it:
e.g. require 'zen-grids'
Finally, add your project into Koala or reload the project.