<?php 

function add_custom_post_type_body_class($classes) {
    // Check if we're in the block editor
    if (is_admin() && function_exists('get_current_screen')) {
        $screen = get_current_screen();
        if ($screen && $screen->post_type) {
            // Add the custom post type class
            $classes .= ' post-type-' . sanitize_html_class($screen->post_type);
        }
    }
    return $classes;
}
add_filter('admin_body_class', 'add_custom_post_type_body_class');