Header Top Sidebar

Is the header top sidebar supposed to be the same dimensions as the site's sidebar? It strikes me that it would be very helpful if it spanned the top of the entire site. I could use that to display special messages (notifications of significant events) or other useful information rather than have it right aligned and limited to the width of the right column. I suppose I could CSS this but as is it seems less useful. What CSS would I use to make the header top sidebar the entire width of the site and center or left aligned?