[css-variables-2][editorial] use correct bikeshed syntax for property values

Author: svgeesus

css-variables-2/Overview.bs

@@ -1098,7 +1098,7 @@ Variable Units</h3>
 	so if the referenced [=custom property=] doesn't exist or is invalid,
 	the unit reference will be invalid as well.
 	Use ''@property'' to create a [=registered custom property=],
-	as the '@property/initial' value will instead be used
+	as the ''@property/initial''' value will instead be used
 	as the default.
 
 	Note: While [=variable unit references=]