Hi, is it possible to modify the button colours, borders etc? And maybe the search box also?
Topic on Extension talk:InputBox
Haven't tried this for the input box, but you can make custom changes to the mediawiki CSS via the MediaWiki:Common.css page. Giving it a quick look the CSS classes your interested in is "mw-ui-button", "mw-ui-input", "mw-ui-input-inline", and possibly "mw-inputbox-centered" for the whole form area. (I just pulled these from the browser via the JS dev tools)
A bit late, but maybe it is useful to you or someone else.
I tried this. Changing MediaWiki:Common.css worked for me.
.mw-inputbox-centered {text-align:left} /* not centered any more */