How to insert the current user's role into the body class in the admin backend

I've tried updating this code from body_class to admin_body_class but it's not inserting the .role-author into the back end body class like it did with the front end body class... i'm guessing it's not as simple as replacing body_class with admin_body_class?

add_filter( 'admin_body_class', function( $classes )
{
    if( is_user_logged_in() )
    {       
        $classes = array_merge( 
            (array) $classes,
            array_map( 
                function( $class )
                {
                    return 'role-' . $class;    // Here we prepend the 'role-' string
                }, 
                (array) wp_get_current_user()-roles 
            )
        );
    }
    return $classes;
} );