Hi all,
we'll enable TemplateStyles [1][2] tomorrow on mediawiki.org, wikitech.wikimedia.org and some test wikis. (Today for those of you in UTC or later time zones.)
TemplateStyles allows editors to add complex CSS to templates with the help of a <templatestyles> tag. This makes template maintenance easier, lowers the barrier of access (previously you had to be an admin to be able to add new CSS) and empowers editors to create more user-, mobile- and print-friendly templates.
For plans for rolling it out to content wikis see T168808 [3].
[1] https://www.mediawiki.org/wiki/Extension:TemplateStyles [2] https://www.mediawiki.org/wiki/Help:TemplateStyles [3] https://phabricator.wikimedia.org/T168808