[css-variables] Clarify language.

Author: tabatkins

css-variables/Overview.bs

@@ -603,7 +603,8 @@ Variables in Shorthand Properties</h3>
 
 	The use of ''var()'' functions in <a>shorthand properties</a> presents some unique difficulties.
 
-	Ordinarily, the value of a shorthand property is separated out into its component <a>longhand properties</a> at parse time,
+	For non-custom properties,
+	the value of a shorthand property is separated out into its component <a>longhand properties</a> at parse time,
 	and then the longhands themselves participate in the <a>cascade</a>,
 	with the shorthand more-or-less discarded.
 	If a ''var()'' functions is used in a shorthand, however,
@@ -670,9 +671,9 @@ Serializing Custom Properties</h3>
 
 	Custom property names must be serialized with the casing as provided by the author.
 
-	<p class='note'>
-		Ordinarily, property names are restricted to the ASCII range and are <a>ASCII case-insensitive</a>,
-		so implementations typically serialize the name lowercased.
+	Note: For non-custom properties,
+	property names are restricted to the ASCII range and are <a>ASCII case-insensitive</a>,
+	so implementations typically serialize the name lowercased.