Several years ago, Jekyll, the open source project that powers GitHub Pages, introduced shared themes. Since then, you have been able to use about a dozen themes to change the look and feel of your GitHub Pages site.
Starting today, you can use any of the hundreds of community-curated themes on GitHub.com. To build your site with any public, GitHub-hosted theme, add the following to your site’s
name with the repository’s owner and name.
And if you’re interested in making your Jekyll theme available to other users, simply follow the instructions for creating a Gem-based theme, and ensure the repository is public.