remove padding from "Define Pages" main_page

Hello,
I hope this is the correct place for this question...

I am using the Define Pages editor to add content (via iframe) to my home page. http://www.sann.net.php5-10.websitetestlink.com/shop/

The iframe works fine, but the problem is that a margin or padding is automatically added to the left and right of the content.

I would like my content (on the home page only) to not have any padding, so that it sits all the way to the left rather than shifted 20px to the right.

Can anyone tell me how/where to remove this padding on just the home page without affecting the rest of my pages??

I guess an alternative could be to build a page outside of zencart and include my zencart header and footer as PHP includes??

If the CSS route is not possible, perhaps someone could help me with the code to implement the above alternative?

Thanks in advance for any help you can provide!