If you’re familiar with GitHub then contributing is simple: just fork and make pull requests. Absolutely everyone is welcome (and even encouraged) to contribute to improve the design of W3C specifications. Bugfixes, code cleanup, and simple improvements will be unilaterally approved by the Design Point Person. For more significant changes to the visual styles, discussion on spec-prod@w3.org is encouraged to get feedback and consensus. (Think of it as a design critique.)

Do not commit directly to any of the common branches (gh-pages and 2016 at the time of writing) unless you are the Design Point Person for the project. Instead, fork the desired branch and submit a pull request.