Popup with scroll bar makes page move rigth

Hi,

Please go to the above page and click on the red ‘Critical Information Summary’ link.

You will see that when the popup opens, the main page content moves to the right.

When i close the popup, the main page content moves to the left.

How do i stop this?

Thanks in advance for your help.

The page I need help with: [log in to see the link]