Background opacity in Slide in

Hi best support ever,
on http://musikzentrale.net i make heavy use of the slide in plugin, displaying our X-mas action. It works great, but there is one thing disturbing user experience: The slide`s bg has a semi-transparent look, so the actual page content is visible to an extent, that makes it hard to read the slider text. I cannot figure out where to get a 100% white opacity, even using firebug. Could you please point me to the right direction? Thank you very much.

cheers, Sebastian