Fix: Ellipsis elements didn't have padding which could be jarring when shifting between paging that does and doesn't show ellipsis
This fixes DataTables/DataTables #26
Previously the CSS shorthand `background` was used for the background of
the header cells, but this makes it a good deal more difficult to set
the background colour if you want to since `transparent` is implicit in
the shorthand used. This method, although a bit longer in CSS is still
fairly simple and a lot more flexible
