Added style class definitions to *Style.d.ts

components/lib/message/style/MessageStyle.d.ts

@@ -1,3 +1,21 @@
+/**
+ *
+ * Message groups a collection of contents in tabs.
+ *
+ * [Live Demo](https://www.primevue.org/message/)
+ *
+ * @module messagestyle
+ *
+ */
 import { BaseStyle } from '../../base/style';
 
+export enum MessageClasses {
+    root = 'p-message',
+    content = 'p-message-content',
+    icon = 'p-message-icon',
+    text = 'p-message-text',
+    closeButton = 'p-message-close-button',
+    closeIcon = 'p-message-close-icon'
+}
+
 export interface MessageStyle extends BaseStyle {}