[css-grid] Clarify that we are growing the base size here. #1120

Author: fantasai

css-grid/Overview.bs

@@ -3953,7 +3953,8 @@ Resolve Intrinsic Track Sizes</h3>
 <h3 id="algo-grow-tracks">
 Maximize Tracks</h3>
 
-	If the <a>free space</a> is positive, distribute it equally to all tracks,
+	If the <a>free space</a> is positive, distribute it equally
+	to the <a>base sizes</a> of all tracks,
 	freezing tracks as they reach their <a>growth limits</a>
 	(and continuing to grow the unfrozen tracks as needed).