2.css is part of the little CSS build process I came up with for this site. There are a bunch of LESS files in a directory (https://github.com/h2s/ppladdressbook.org/tree/master/_style...). Then there's a rake task to build them into {{site.version}}.css. This means I can update the CSS, bump the version number, run jekyll, and push the changes live being certain that there won't be any annoying caching issues stopping people from getting the updated CSS.