[css-flexbox-1] Clarify that we're only talking about the cross-sizes of the items here. #3531

Author: fantasai

css-flexbox-1/Overview.bs

@@ -2981,8 +2981,9 @@ Definite and Indefinite Sizes</h3>
 
 		<li>
 			Once the cross size of a flex line has been determined,
-			items in auto-sized flex containers are also considered
-			definite for the purpose of layout; see <a href="#algo-stretch">step 11</a>.
+			the cross sizes of items in auto-sized flex containers
+			are also considered definite for the purpose of layout;
+			see <a href="#algo-stretch">step 11</a>.
 	</ol>
 
 	Note: The main size of a <a>fully inflexible</a> item with a <a>definite</a> <a>flex basis</a>