#toplevel_page_rg-slider .wp-menu-image {
  background: url("../img/menu-icon.png") no-repeat 1px -33px;
}
#toplevel_page_rg-slider:hover .wp-menu-image {
  background: url("../img/menu-icon.png") no-repeat 1px -1px;
}
#toplevel_page_rg-slider.wp-has-current-submenu .wp-menu-image {
  background: url("../img/menu-icon.png") no-repeat 1px -1px;
}