If you started a project like CSS Zen Garden today, it would be natural to put the source code on GitHub and ask for contributions via pull request. However, CSS Zen Garden just turned 10, so its life spans beyond that of Git and GitHub for that matter.
So, needless to say, it's a big deal for Dave Shea to move the codebase to GitHub and follow suit with what we now think is a norm, which is open projects and social coding.
If you'd like to add a modern CSS Zen Garden design to the mix, fork, branch and submit a pull request! If you're new to Git and GitHub, and you're not sure what to do - either learn git (do this!) or use the traditional submission form at mezzoblue.com/zengarden/submit.
Sadly my submission from WAY BACK IN THE DAY was never added as an official design, but can be seen (un-styled) here. I still have the CSS for that so maybe one day I can work it out with Dave to update the CSS src URL for my submission.