background-image doesn't appear if is empty?

Answer 1

Since the div is empty, there's no content to push it "open" leaving the div to be 0px tall. Set explicit dimensions on the div and you should see the background image.

.bordertop 
{
    background-image: url(../images/top_border.png);
    background-repeat: repeat-x;    
    height: 100px;
    width: 100%; /* may not be necessary */
}