.wp_themeSkin span.mce_embedpluswiz, span.mce_embedpluswiz
{
    background: transparent url("btn_embedpluswizoff.png") no-repeat scroll center center !important;
}

.wp_themeSkin span.mce_embedpluswiz:hover, span.mce_embedpluswiz:hover
{
    background-image: url("btn_embedpluswiz.png") !important;
}