[css-color-5] Simplify contrast-color(), per WG resolution. #11534 (#11654)

Author: tabatkins

css-color-5/Overview.bs

@@ -2606,23 +2606,17 @@ or any other color or monochrome output device which has been characterized.
 	the surrounding colors, etc.
 
 	<pre class='prod'>
-		<dfn export>contrast-color()</dfn> = contrast-color( <<color>> max? )
+		<dfn export>contrast-color()</dfn> = contrast-color( <<color>> )
 	</pre>
 
-	If ''max''' is specified, the function computes to ''white'' or ''black'',
-	depending on which of the two produces _maximum_ color contrast for text when the input color is used as a solid background.
-	If both colors produce the same contrast, the function should return ''white''.
-
-	If ''max''' is omitted, the function computes to a <em>very light</em> or <em>very dark</em> color (which <em>may</em> still be white or black),
-	which will contrast well with the input color when used as a text color and the input color is used as a solid background.
-	The function MUST return a light color if it would have returned ''white'' if ''max'' were specified,
-	and a dark color if it would have returned ''black'' if ''max'' were specified.
-
-	Note: The precise requirement for how close these colors need to be to white and black
-	and what color difference measure to use for that are still under discussion.
+	''contrast-color()'' resolves to either ''white'' or ''black'',
+	whichever produces <strong>maximum</strong> color contrast for text 
+	when the input color is used as a solid background.
+	If both ''white'' and ''black'' produce the same contrast,
+	it resolves to ''white''.
 
 	The precise color contrast algorithm for determining whether to output a light or dark color
-	is UA-defined at this level, as is the precise color produced when ''max''' is omitted.
+	is UA-defined at this level.
 
 	Note: Future versions of this specification are expected to introduce more control over
 	both the contrast algorithm(s) used, the use cases, as well as the returned color.