Principles

Everything should be 100% responsive

Your website should be readable and work regardless of a users device or screensize. Don't break the functionality of HTML with CSS.

Everything should be readable on any device

Just because it's readable to you on your laptop, doesn't mean it is readable by your users. Make sure your type is big. Make sure your contrast is high.

Everything should be as performant as possible

Code isn't for making a developers life easier. It's for improving the lives of our users. If it's not doing that, why write it. A developer's time is not precious. A user's time is.

Designing in the browser should be easy

If a computer can do it, you shouldn't have to.

Doing one thing extremely well promotes reusability

Single purpose classes that are easy to grock.

Features

Built on Rework

A flexible plugin framework for preprocessing css. View on Github

Mobile-first css architecture

Base classes are mobile by default. Can be overridden by namespaced classes targeting larger breakpoints.

Default colors for rapid theming

Who cares about colors. Unless you're painting a bikeshed.

CSS layout debugging utilities.

Small css modules for debugging stacking and layout issues. Can easily be turned on or off during development.

Composable class names

Scale based design system

Powers of two. Starting at .25

Easy to customize and extend

Take what you need. Leave the rest. The small single-purpose modules make it easy to grab only what you need without needing to figure out dependencies.