Hi,
CSSJanus is now[1] included in MediaWiki core through composer, and maintained as an external library on Github[2].
Running "composer update" will download and autoload the library, or if you're using the mediawiki/vendor repository a simple "git pull" will work.
-- Legoktm
[1] https://gerrit.wikimedia.org/r/170107 [2] https://github.com/cssjanus/php-cssjanus