Thank you that worked.
One more question:
How can I get the two adverts to stay together at the top of the page on mobile devices?
At the moment the advert on the left stays at the top of the page on small devices, this is then followed by the main content, and below that is the advert from the right of the page.
As you can imagine, the advertiser in sidebar-1 position would not be too happy if their advert is pushed to the bottom of the page on small devices.
Can this template control positioning of the sidebars on small devices so both are above the main content?