CSS style guides maintained by companies
Style guides written and maintained by top tech companies
Airbnb
A mostly reasonable approach to CSS and Sass
Dropbox
Dropbox’s (S)CSS authoring style guide
WordPress
A baseline for collaboration and review within various aspects of the WordPress open source project and community
This document defines formatting and style rules for HTML and CSS
Bootstrap
Standards for developing consistent, flexible, and sustainable HTML and CSS.
ThinkUp
This is the Code Style guide for CSS
Workable
This is the coding style guide we use for writing CSS & Sass in Workable.
CodePen
Inspired by Mark Otto's tour of GitHub's CSS and Ian Feather's tour of Lonely Planet's CSS