Create new Text Editor - D8

Hi there,

I need to add CSS and JS files to some Textareas, so I'm trying to create new Text Editor.

Following this article https://www.drupal.org/docs/8/api/text-editor-api

Inside my module I've created a file: src\Plugin\Editor\MyEditor.php with the default text:

<?php

namespace Drupal\my_editor\Plugin\Editor;

use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Render\Element;
use Drupal\Core\Render\RendererInterface;
use Drupal\editor\Plugin\EditorBase;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\editor\Entity\Editor;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Defines a CKEditor-based text editor for Drupal.
 *
 * @Editor(
 *   id = "MyEditor",
 *   label = @Translation("MyEditor"),
 *   is_xss_safe = FALSE,
 *   supported_element_types = {
 *     "textarea"
 *   }
 * )
 */
class MyEditor extends EditorBase{

}

As result, I can see my editor on the Format settings page under the "Text Editor" selectbox, but I got error
You must configure the selected text editor.
if I select MyEditor and save the form.

How to solve this problem? May be there is easies way to add CSS and JS styles for some TextFormats?

Thanks.