[css-sizing] Fix awkwardly-branching sentence.

Author: tabatkins

css-sizing/Overview.bs

@@ -346,8 +346,9 @@ Intrinsic Sizes of Replaced Elements</h3>
 		calculated with an unconstrained specified size.
 
 	The <a>min-content contribution</a> and <a>max-content contribution</a> in each axis
-	is the element's specified outer size in that axis, if definite,
-	and the <a>min-content size</a>, as specified above, plus the element's margin/border/padding in that axis otherwise,
+	is the element's specified outer size in that axis, if definite;
+	otherwise, they are the <a>min-content size</a>, as specified above,
+	plus the element's margin/border/padding in that axis,
 	clamped by the element's min and max size properties in that axis.
 
 <h3 id='inline-intrinsic'>