#theory_hover
{display: block; width: 115px;height: 15px;background: url("images/menu_button_theory.gif") no-repeat 0 0;}
#theory_hover
{background-position: 0 -15px;}
#theory_hover span
{display: none;}
#theory_hover:hover
{background-position: 0 -15px;}
#theory_hover span
{display: none;}