 <p>You should first learn about <a href="http://sass-lang.com/guide" rel="nofollow"><em>SASS</em></a></p> <p>You will see that SASS is actually CSS made easy and with more features like the ability to use Variables : <code>$myHeight : 500px;</code></p> <p>In your example, he is using variable.</p> <p>To inject it in your project, you need to find a way to save your SASS file in a CSS file. In the above link it is using the command</p> <blockquote> <p>sass --watch app/sass:public/stylesheets</p> </blockquote> <p>But you can also do it with grunt or <a href="https://www.npmjs.com/package/gulp-sass" rel="nofollow">gulp</a></p>