@mdo also created Twitter Bootstrap. Primer is a pure CSS framework - no JavaScript. Currently, primer.css file is only 30.8k uncompressed!

Primer is GitHub’s internal CSS toolkit. It’s been the base coat for GitHub.com for years now, providing styles for our global typography, layout, tooltips, buttons, and more. Starting today, it’s open source.

Primer isn’t another large front-end framework, though. It’s rather limited in functionality and isn’t intended to replace something like Bootstrap. It will always be GitHub’s internal toolkit first, designed to help build GitHubby things. That said, we love to share.

Primer is licensed MIT, so you can basically do whatever you like with the source code. We’ll be a little stringent on merging new features to the project for the foreseeable future though. Longer term, we envision having a suite of Primer projects—one repository for each new component. More on that another time though.

For now, head to GitHub to view the source code and read through the docs at http://primercss.io.

“Standards for developing flexible, durable, and sustainable HTML and CSS.”

How to order attributes, how to write CSS declarations like a gentleman, etc.

I’m always interested in the development details of other products, particularly their styleguides and approach to CSS. Given my penchant for the otherwise inane CSS details, I decided to write a bit about GitHub’s CSS.

Contents

Given the length, here’s a helpful table of contents.

Quick facts

Preprocessor

Architecture

Linting

Two bundles

Included via Sprockets

Performance

Documentation

Primer