lf designs on "[Theme: Customizr] Background for individual pages"

Hello all,

I've been looking for solutions for a couple of days now and, although not 100% sure there aren't any out there, I'm going to start a new thread.

My in-progress website is here: jabutitheatre.com

I'm trying to get a background for individual pages (in this case starting with projects>my city.
The background is currently throughout the site.

I tried with:

/* Set an image in the internal body */
#main-wrapper {
background: 	url(/wp-content/themes/uploads/mycity_background.png);
margin-top:     0px ;
margin-bottom:  0px;
}

as well as:

#main-wrapper.page-id-123 {
background: 	url(/wp-content/themes/uploads/mycity_background.png);
margin-top:     0px ;
margin-bottom:  0px;
}

or even:

body.page-id-123 {
background: 	url(/wp-content/themes/uploads/mycity_background.png);
margin-top:     0px ;
margin-bottom:  0px;
}

None have worked. I'm not sure why and I've not found anything on this in the forum apart from one which gave me the hint of using the page id, but it doesn't seem to work.

hope for some guidance.

thanks!