I'm pretty sure I fixed this bug at least three times in the past, and @Esanders fixed it once or twice too.

This'd be because @Esanders removed the hack that accounted for Vector's high #p-personal z-index in efd41fbc74dd24874a79dbe0c29443bc03dc83c4. That commit says that Vector should have had its z-index fixed, but presumably that hasn't actually rolled out?

In T127742#2072496, @DLynch wrote:

This'd be because @Esanders removed the hack that accounted for Vector's high #p-personal z-index in efd41fbc74dd24874a79dbe0c29443bc03dc83c4. That commit says that Vector should have had its z-index fixed, but presumably that hasn't actually rolled out?

The Vector fix was 1cce1de1be93ed7fdad00155d117596d11402e73 and was rolled out at the same time, but apparently isn't working.

I'd guess that "+oojs-ui.styles": "skinStyles/ooui.less", is failing to trigger ooui.less's inclusion on VE pages, though I'm not actually familiar enough with ResourceLoader to know quite where the fix for that should lie.

Argh, we renamed that module…

Change 273931 had a related patch set uploaded (by DLynch):
oojs-ui.styles is now oojs-ui-core.styles

https://gerrit.wikimedia.org/r/273931

Change 273931 merged by jenkins-bot:
oojs-ui.styles is now oojs-ui-core.styles

https://gerrit.wikimedia.org/r/273931