Transparent Center Area

Hi Everyone,

I'm currently trying to figure out how to get the center area of my page to have a slight transparency so the background image will show through, I don't want the header or footer to be transparent. Any ideas on how to accomplish this? I can make the whole page transparent but that's no help unfortunately. I'm trying to find out the right html tag so I can put it in "add html/css inserts" You can see my site at: campgilwell.ca

Kindest Regards