The quick action hint in CKEditor lacks contrast

Okay, since it's a UI bugfix it also makes sense to only create a RN documentation.

Note that https://extensions.xwiki.org/xwiki/bin/view/Extension/CKEditor%20Integration/#HQuickActions shows the hint but never describes it. Since our only change is visual, and it looks pretty similar, I think it's alright to not update the videos. Those videos look a bit old (save/cancel buttons have shadows and highlights) but there's definitely worst so IMO we still have a bit of time before updating them