Adjust for border with box-sizing: border-box
Adjust for border with box-sizing: border-box

Inner height is now 2em-2px so adjust grip position
by -1px to centre correctly.

Change-Id: Id11a043b10bf1c1591cb5a51533c34abbb4c79fc

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui