Add classes to the Gutenberg iframe (editor-canvas) body tag?

I believe Gutenberg content was iframed in WP 6.2 if all blocks are v3 (?). I have used a function like below to add?very important?custom classes to my admin body tags which in turn alters how the content is presented. This is important for layout and consistency.

add_filter('admin_body_class', function ($classes) {
    global $pagenow;

    //check if the current page is post.php and if the post parameters set
    if ( $pagenow ==='post.php' || $pagenow ==='post-new.php' ) {
        global $post;
        
        /* ... */

        $classes .= ' super-important-editing-class';
        
    } 

    return $classes;
});

I’ve searched like crazy to find a filter which makes me do the same thing on the iframes body tag ('block-editor-iframe__body editor-styles-wrapper ...').

Does anyone know a way to do this?