The CSS Starter contains components and patterns for building pure CSS UI. It is not a CSS framework!
To build a site with the CSS starter, start from scratch with only a reset and a blank CSS file. Build your styles as you build your markup. Pull styles, markup, and patterns from the starter as you need them. As your styles differ from the starter styles, modify the styles rather than overriding them.
Read more and see it in action at starterapp.style.