Adding separator between posts

http://www.shaunhillphotography.co.uk/news/

Hello all, I am trying to insert custom css code which automatically enters a separator between posts, but not having much luck.

I don’t know how to select a class within an id:

entry-utility #content-sm{
background: url(http://img367.imageshack.us/img367/1606/damasksplitterbgsd8.gif) no-repeat;
height: 100px;
width: 1000px;
}