display: overflow: and position:fixed all together

[david.ledger]

I have a product fabric selection popup pane that is a layer that is revealed and hidden by JavaScript. It works fine, but when the product page is long the user may have to scroll up to find the popped-up pane.To make it easier I would like to make the popup position:fixed. If I do that and the popup itself gets long, I need to have overflow:scroll on the popup so the user can reach it all. When I experiment the display:block seems to stop working as the popup doesn't reveal.What are the tricks I need to make these three work together please?David