Block Editor CSS

/*
 * Block Editor Style - Gutenberg
 */
add_action( 'after_setup_theme', function() {

	add_theme_support( 'editor-styles' ); // wichtig - entspricht nicht dem Filename des CSS Files
	add_editor_style( trailingslashit( get_stylesheet_directory_uri() ) . 'editor-style.css' );

} );

Weiterführende Links:

• https://rudrastyh.com/gutenberg/css.html
• https://css-tricks.com/getting-the-wordpress-block-editor-to-look-like-the-front-end-design/
• https://wpblockz.com/tutorial/register-block-styles-in-wordpress/