Note: After saving, you have to bypass your browser's cache to see the changes. Internet Explorer: press Ctrl-F5, Mozilla: hold down Shift while clicking Reload (or press Ctrl-Shift-R), Opera/Konqueror: press F5, Safari: hold down Shift + Alt while clicking Reload, Chrome: hold down Shift while clicking Reload.
#wpTextbox1{height:35em;}/* Display full thumbnails in Special:Search, again. Thank you, Tuvalkin, for this workaround */.searchResultImage-thumbnail.mw-file-descriptionimg{object-fit:contain;object-position:center;border:none;}