Sass

• http://sass-guidelin.es
• http://sassdirector.com

Contrast

• http://madebymike.com.au/writing/accessible-contrast-with-less-and-sass/
• https://github.com/voxpelli/sass-color-helpers

LibSass

sudo apt-get install build-essential git
git clone https://github.com/sass/libsass
make

Ubuntu

• https://www.digitalocean.com/community/tutorials/how-to-install-ruby-on-rails-on-ubuntu-12-04-lts-precise-pangolin-with-rvm

sudo apt-get update
sudo apt-get install curl
curl -L https://get.rvm.io | bash -s stable
source ~/.rvm/scripts/rvm
rvm requirements
rvm install ruby
rvm use ruby --default
rvm rubygems current

gem install sass
sass -v