background image to modules Advert1 to 4

How can I add a background image to modules Advert1 to 4?
I tried to add background-image to the css but it doesnt work

#c1,#c2,#c3,#c4,#c5,#c6,#c7,#c8 {
margin-right:3px;
padding:15px 0 5px 0;
background-image:url(/images/upper_background.jpg);
}

add suffix to module with first blank ckar like this, example advert1:

" adv1_class"

then at template_css.css at bottom add:

.adv1_class{
background:...
}

Thank you for the reply. This is not exactly what I wanted. The image does not fill the whole module background. You can check this at new.fcpaok.gr

any other solution?

Then use:

#c5,#c6,#c7,#c8 {
background:...!important;
}

don't forget to add !important flag