CSS Positioning - Expert needed

We would like to add an advertising right to a centered responsive website. Therefore we created a div-tag and tried to find the right positioning via CSS. But we didn't get it. See the test-site: [login to view URL] There you find the grey box in the right. The issue: if you have a resolution of 1920px the grey box is well positioned. If you have a smaller resolution the grey box changes position. We would like to see it always 10px right to the border of the main content. Note: we need an invoice.