The search button with the magnifying glass has attributes width and height. These attributes are no longer valid in HTML5 [1][2] and should be replaced by CSS.

[1] http://www.w3.org/TR/html5/the-button-element.html#the-button-element
[2] http://validator.w3.org/check?verbose=1&uri=https%3A%2F%2Fwww.mediawiki.org%2Fwiki%2FMediaWiki - last two errors

Version: 1.21.x
Severity: minor