silverstripe-userforms/docs/en/compiling-front-end-files.md

Compiling Front-End Files

UserForms stylesheets are written in SASS, so to make changes you'll need to have Compass installed.

Debian/Ubuntu

$ apt-get update
$ apt-get install ruby
$ gem install compass

OSX

Install homebrew. Then:

$ brew update
$ brew install ruby
$ gem install compass

Compile assets

Make your changes to scss/UserForm.scss or scss/UserForm_cms.scss. Then navigate to the userforms folder and run:

$ compass compile