#adminmenu #toplevel_page_orderguard .wp-menu-image {
    background-image: url(../orderguard-shield.svg);
    background-repeat: no-repeat;
    background-position: center center;
    background-size: 24px auto;
    filter: brightness(0) invert(1);
    opacity: 0.6;
}

#adminmenu #toplevel_page_orderguard:hover .wp-menu-image,
#adminmenu #toplevel_page_orderguard.current .wp-menu-image,
#adminmenu #toplevel_page_orderguard.wp-has-current-submenu .wp-menu-image {
    opacity: 1;
}