--- /dev/null
+<?php
+
+namespace Drupal\ckeditor\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command to add style sheets to a CKEditor instance.
+ */
+class AddStyleSheetCommand implements CommandInterface {
+
+ /**
+ * The CKEditor instance ID.
+ *
+ * @var string
+ */
+ protected $editorId;
+
+ /**
+ * The style sheet URLs to add to the CKEditor instance.
+ *
+ * @var string[]
+ */
+ protected $styleSheets = [];
+
+ /**
+ * AddStyleSheetCommand constructor.
+ *
+ * @param string $editor_id
+ * The CKEditor instance ID.
+ * @param string[] $stylesheets
+ * The style sheet URLs to add to the CKEditor instance.
+ */
+ public function __construct($editor_id, array $stylesheets = []) {
+ $this->editorId = $editor_id;
+ $this->styleSheets = $stylesheets;
+ }
+
+ /**
+ * Adds a style sheet to the CKEditor instance.
+ *
+ * @param string $stylesheet
+ * The style sheet URL.
+ *
+ * @return $this
+ * The called object, for chaining.
+ */
+ public function addStyleSheet($stylesheet) {
+ $this->styleSheets[] = $stylesheet;
+ return $this;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function render() {
+ return [
+ 'command' => 'ckeditor_add_stylesheet',
+ 'editor_id' => $this->editorId,
+ 'stylesheets' => $this->styleSheets,
+ ];
+ }
+
+}