refactor(css‑variables): Simplify var() function syntax definition

Author: ExE-Boss

css-variables-1/Overview.bs

@@ -393,7 +393,7 @@ Using Cascading Variables: the ''var()'' notation</h2>
 	The syntax of ''var()'' is:
 
 	<pre class='prod'>
-	<dfn>var()</dfn> = var( <<custom-property-name>> [, <<declaration-value>> ]? )
+	<dfn>var()</dfn> = var( <<custom-property-name>> , <<declaration-value>>? )
 	</pre>
 
 	The ''var()'' function can be used in place of any part of a value in any property on an element.