Update css-view-transitions-1/Overview.bs

Co-authored-by: Khushal Sagar <63884798+khushalsagar@users.noreply.github.com>

Author: vmpstr

css-view-transitions-1/Overview.bs

@@ -1119,7 +1119,7 @@ The {{ViewTransition/domUpdated}} [=getter steps=] are to return [=this's=] [=Vi
 
     1. Let |callbackPromise| be [=a new promise=] in |transition|'s [=relevant Realm=].
 
-        * If it is null, then resolve |callbackPromise|.
+        * If |transition|'s [=ViewTransition/DOM update callback=] is null, then resolve |callbackPromise|.
 
         * Otherwise, let |callbackPromise| be the result of [=/invoking=] |transition|'s [=ViewTransition/DOM update callback=].