I have developed a modal image box which is working as desired except for one thing.  I can't get the background div to cover the entire window background when the backgroud extends beyond the visible window size (requiring vertical scrolling).   The background will only fill to the size of the the visible window area.  If I scroll the window while the modal box is showing the lower area is exposed.  I have the background div height set to 100%.  I have tried min-height: 100%.  I have also just made the height a really big number which causes the page to expand too.   I guess I am asking how this is done in the JQuery UI dialog which works just fine on the same page.