making the background of the jqm dialog box transparent?

making the background of the jqm dialog box transparent?

http://creative.coventry.ac.uk/~4089797/Games/V2.0/test.html

Heres my site so far

Im trying to make the menu dialog popup but still allow the previous page to be seen in the background around the dialog box but have no idea where to start. Ive looked at documentation but havent been able to make sense of which bits i need?