li#toplevel_page_o365-wp-restrict .wp-menu-image:before {
    width: 20px;
    background-image: url(../img/o365-plu.png);
    background-size: 19px;
    height: 20px;
    display: inline-block;
    background-repeat: no-repeat;
    margin: 6px 0 0 5px;
    cursor: pointer;
    content: '';
}