Its conscise but well commented. No excess stuff, only the essentials.
Girder works with Node-Sass or Ruby Sass and easily adapts to your needs.
The grid likes relative units, it supports media queries and you can build mobile-first.
With Bower just use: "bower install girder --save" and add a reference to either scss/_girder.scss or girder.css inside the components folder.
@import the _girder.scss partial which should reside next to its modules in your project.
Simply include girder.css in your document along with the site's styles. (Like this page)
For more tips on using Sass and Girder check out the journal.