in case you want to view the repo, it's linked in the https://atlaskit.atlassian.com/ (menu -> resources).
The breadcrumb to get to it is a bit crazy, but https://bitbucket.org/atlassian/design-system-mirror/src/mas... is the old mirror, which has a link in the readme to the new mirror: https://bitbucket.org/atlassian/atlassian-frontend-mirror/sr...
Except going to https://bitbucket.org/atlassian/atlaskit/src/master tells you to go to https://bitbucket.org/atlassian/atlaskit-mk-2/src/master/ which then tells you:
> Unfortunately, that code no longer resides here as it’s all been moved to a new closed source location.