The default bundle of Mobi.css provides the basic styles to build clean and elegant webpages. It's only 3kb after gzipped, and it's very easy to get started.
Plugin system makes css scalable. You can import plugins to enhance Mobi.css, or use the plugin as a standalone css library. It's even possible to use a plugin without Mobi.css.
Mobi.css focus on the details and provides the best user experience, especially for content-rich webpage. It's designed for mobile, but also works awesome on desktop.