[css-grid-2] Add missing word in sentence. #7070

Author: fantasai

css-grid-2/Overview.bs

@@ -3664,7 +3664,7 @@ Subgrids</h2>
 
 		<li id="subgrid-item-contribution">
 			The <a>subgrid</a>'s own <a>grid items</a> participate
-			in the sizing of its in the [=subgridded=] dimension(s)
+			in the sizing of its [=parent grid=] in the [=subgridded=] dimension(s)
 			and are aligned to it in those dimensions.
 
 			<p id="subgrid-margins">