need to add wrapper to popup windows

I have ZC 1.3.9g running on Linux grid host at Go Daddy.
My stylesheet.css has a background image I have added. The result is that the spaces around the main wrapper looks like tiles.
My problem is the shipping estimator popup does not have a wrapper so the text is displayed over the background image of tiles and is unreadable. I am thinking that near the bottom of the stylesheet.css I need to add '#popupShippingEstimator' to include a wrapper.
I am not great with css and am not sure what or where to add to make a wrapper.

I found a solution thats easier.
in stylesheet.css scroll near the bottom and find the following:

#popupShippingEstimator, #popupSearchHelp, #popupAdditionalImage, #popupImage, #popupCVVHelp, #popupCouponHelp, #popupAtrribsQuantityPricesHelp, #infoShoppingCart

I added
'background-image: none;' just above the background color line.
The background color used to be over written by the image defined in the 'body' (top of stylesheet.css).