找到了这个，但它真的应该在WordPress核心中：

// Body class for admin
// http://www.kevinleary.net/customizing-wordpress-admin-css-javascript/
function base_admin_body_class( $classes )
{
    // Current action
    if ( is_admin() && isset($_GET[\'action\']) ) {
        $classes .= \'action-\'.$_GET[\'action\'];
    }
    // Current post ID
    if ( is_admin() && isset($_GET[\'post\']) ) {
        $classes .= \' \';
        $classes .= \'post-\'.$_GET[\'post\'];
    }
    // New post type & listing page
    if ( isset($_GET[\'post_type\']) ) $post_type = $_GET[\'post_type\'];
    if ( isset($post_type) ) {
        $classes .= \' \';
        $classes .= \'post-type-\'.$post_type;
    }
    // Editting a post type
    $post_query = $_GET[\'post\'];
    if ( isset($post_query) ) {
        $current_post_edit = get_post($post_query);
        $current_post_type = $current_post_edit->post_type;
        if ( !empty($current_post_type) ) {
            $classes .= \' \';
            $classes .= \'post-type-\'.$current_post_type;
        }
    }
    // Return the $classes array
    return $classes;
}
add_filter(\'admin_body_class\', \'base_admin_body_class\');