PHP显示无？

I'm trying to hide the "topbar" if user is logged in. Example: http://prntscr.com/chcwhl

My code at the moment is:

add_filter( 'wp_nav_menu_items', 'woohoo_add_auth_links', 10 , 2 );
function woohoo_add_auth_links( $items, $args )
{
    if( $args->theme_location == 'topmenu' )
    {
        if ( is_user_logged_in() ) {
            echo '<style>#topbar { display:none;}</style>';
        }
        elseif ( !is_user_logged_in() ) {
            $items .= '<li><a href="'. site_url('wp-login.php') .'">Log In</a></li>';
            $items .= '<li><a href="'. site_url('wp-login.php?action=register') .'">Register</a></li>';
        }
    }
    return $items;
}

I'm sure that the topbar is <div class="topbar"> so I'm a little confused why it's not hiding...

The # means ID. You can fix this by either using:

<div id="topbar">

Or:

echo '<style>.topbar { display:none;}</style>';

A # is css for ID, and a . is css for class.