right now if you don't mind pre-release code: browse source: http://core.trac.wordpress.org/browser/trunk/wp-content/themes/twentytwelve check it out:

right now if you don't mind pre-release code: browse source: http://core.trac.wordpress.org/browser/trunk/wp-content/themes/twentytwelve check it out: svn co http://core.svn.wordpress.org/trunk/wp-content/themes/twentytwelve /path/to/your/themes/dir/twentytwelve