[css-conditional-5] Add a <dfn> to fix a fatal bikeshed error about algorithm.

Author: dbaron

css-conditional-5/Overview.bs

@@ -1453,7 +1453,7 @@ Style Container Features</h3>
 	for the given [=property=].
 
 	<div algorithm>
-		To evaluate a <<style-range>>,
+		To <dfn noexport>evaluate a <<style-range>></dfn>,
 		the following steps needs to be performed:
 
 		1. If <<style-range-value>> is a <<custom-property-name>>,