I'm afraid that it's not possible by changing css because there are a few <td> elements between tabs and you neither are able to set their css neither remove them.
You helped me to open up my eyes I tried everything in improper place .
How about using jQuery, use the following code to remove the spacer tab from them-
<a4j:loadScript src="resource://jquery.js" />
Let me try.
Thanks & Regards,