Problem: We load lots of mediawiki.ui styles as render blocking, but they do not need to be render blocking.
We will load most of mediawiki.ui.button via JavaScript. This will trim down initial CSS by up to 0.7kb.
Minerva will load a lightweight CSS module which simply provides the basic CSS for the button.
@Volker_E and I took a look at mediawiki.ui.button usage and Minerva and special pages are the only things that use this code without JavaScript.
= Acceptance criteria
[] Make sure a minimum render blocking module mediawiki.ui.lite is loaded on all pages
[] Make sure the basic mediawiki.ui.lite module is loaded on Special:MobileWatchlist pages without JavaScript and the full mediawiki.ui.button module is loaded with JavaScript.
[] Make sure mediawiki.ui.button is loaded via JavaScript on all content pages