[css-sizing-3] Tweak wording, attempt 2. #2315

Author: fantasai

css-sizing-3/Overview.bs

@@ -522,9 +522,9 @@ Box Edges for Sizing: the 'box-sizing' property</h3>
 	Animation type: discrete
 	</pre>
 
-	The 'box-sizing' property switches the box model
-	between assigning fixed sizes such as <<length>>s and <<percentage>>s
-	to the <a>content box</a> and the <a>border box</a>.
+	The 'box-sizing' property defines whether
+	fixed sizes (such as <<length>>s and <<percentage>>s)
+	are assigned to the <a>content box</a> or to the <a>border box</a>.
 	It affects the interpretation of all <a>sizing properties</a>,
 	including 'flex-basis'.