Try replying to any Flow post - e.g., this one: https://www.mediawiki.org/w/index.php?title=Talk:Sandbox&topic%5BpostId%5D=050f698e3f6e5624fa1590b11c27932f&workflow=050f698e3f6e5624fa1590b11c27932f
Before you start typing, when the button is not active, it's smaller than when you start typing and it becomes active – apparently due to a border that appears in the active state. In context, this causes the rest of the buttons in that row to jump a bit and generally looks a bit janky.
Version: master
Severity: normal