I have made a patch for a responsive version of MonoBook with mobile support. See: https://gerrit.wikimedia.org/r/c/421199/ or if you just want a live demo, https://wiki.zaori.org/wiki/Page_title?useskin=monobook - load it on a phone or make your browser window narrow or something and you can see what it looks like. This is a prototype nojs version; I intend to make an even sillier js layout with popovers and stuff as a followup patch.
A potential issue has already been raised with the icons: I don't really know how to make text strings actually, well, reliably fit on mobile devices, but a lack of support for no-image usage could also be a real problem in MonoBook. Feedback on that or whatever, as well as other testing and reviews, would be greatly appreciated.
There is also a rather more immediate problem at present. As you can see on the patch, jenkins has -1ed it for style problems. Unfortunately I have no idea what the style problems are because the output of that test is totally useless (https://phabricator.wikimedia.org/T190072) - can anyone tell me what the problem(s) are so I can fix them? And/or just resolve T190072? Please? It's starting to get a bit annoying, frankly, as it's been coming up across several of these patches.
-I