office-js: add OfficeThemeChanged event

types/office-js/index.d.ts

@@ -1974,6 +1974,14 @@ declare namespace Office {
          * Triggers when a customXmlPart node was replaced.
          */
         NodeReplaced,
+        /**
+         * Triggers when the OfficeTheme was changed in Outlook.
+         * 
+         * [Api set: Mailbox Preview]
+         * 
+         * @beta
+         */
+        OfficeThemeChanged,
         /**
          * Triggers when the recipient list of the selected item was changed in Outlook.
          * 
@@ -14782,9 +14790,7 @@ declare namespace Office {
         /**
          * Adds an event handler for a supported event.
          *
-         * Currently the only supported event type is Office.EventType.ItemChanged, which is invoked when the user selects a new item. 
-         * This event is used by add-ins that implement a pinnable taskpane, and allows the add-in to refresh the taskpane UI based on the currently 
-         * selected item.
+         * Currently the supported event types are `Office.EventType.ItemChanged` and `Office.EventType.OfficeThemeChanged`.
          *
          * [Api set: Mailbox 1.5]
          *