I'm sure you know that when you include things you include just the code needed for the include. So if you have a menu in a special table your include file will look like this:
<table>
<tr>
<td>
... Menu
</td>
</tr>
</table>
Since CSS has to be defined in the head of the document -- either as an external <link> or internal <style> you will notice that there is no possiblity to have css in the include file. Since you are including this, you could define the css inline by doing:
<table style="your css;">
but this technique is not recommended. Also, if you have a lot of css for a lot of elements your code will be hard to read. What is wrong with defining css in the head of the document you're including to? Since includes are done server side, when the page is served to the client it is a simple html page. If you have many pages into which you include this menu and was thinking of simplifying the process by having just one css for all of them, you can still do that by referencing external stylesheet via <link> in the head.
As for the scrollbar in a frame, I don't know. Do you have a sample page? I have tested it here and all the frames have custom scrollbars.