Dreamweaver: Change background image of spry menu bar

I want to add a background image to the main spry menu. I have the following .CSS code that does not work:

ul.MenuBarHorizontal
{
      margin: 0;
      padding: 0;
      list-style-type: none;
      font-size: 100%;
      cursor: default;
      width: auto;
      background-image: url(../images/buttons/Button_Normal.png) no-repeat;
}