[css-color-4] Opacity property now uses opacity-value (which has different clamping behavior to alpha-value)

Author: svgeesus

css-color-4/Overview.bs

@@ -600,7 +600,7 @@ Transparency: the 'opacity' property</h3>
 
 	<pre class=propdef>
 	Name: opacity
-	Value: <<alpha-value>>
+	Value: <<opacity-value>>
 	Initial: 1
 	Applies to: all elements
 	Inherited: no