Noticed on mediawiki.org, currently at 1.23wmf2 (rMW88c7b3fee763)
On hover, the Help icon in the VisualEditor toolbar gets both the light gray border with all corners rounded, and the darker gray border that, if I look at the Menu icon for reference, should probably only appear when the button is pressed, not just hovered.
Furthermore, the dark gray border only has the left corners rounded.
Version: unspecified
Severity: trivial