MediaWiki UI: Adjustments to mw-ui-input

Correcting slight issues with mw-ui-input with
focus behaviour and vertical alignment

Use negative margin to ensure that when input element is
focused that all 4 border sides are shown rather than just
3.

Change-Id: I9d51fcd1781a9a615e3b41e6988e19021466a9d1
Merge "MediaWiki UI: Adjustments to mw-ui-input"