[css-color-adjust-1] Rewrite color forcing section.

Author: fantasai

css-color-adjust-1/Overview.bs

@@ -330,9 +330,9 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 
 	When <a>forced colors mode</a> is active
 	and 'forced-color-adjust' is ''forced-color-adjust/auto'' (see below) on an element,
-	colors on the element must be force-adjusted to the user’s preferred color palette.
+	colors on the element are force-adjusted to the user’s preferred color palette.
 
-	For each of the following properties:
+	Specifically, for each of the following properties:
 
 	<ul>
 		<li>'color'
@@ -345,31 +345,36 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		<li>'column-rule-color'
 		<li>'scrollbar-color'
 		<li>'-webkit-tap-highlight-color'
-	</pre>
+		<li>'background-color'
+	</ul>
 
-	if the [=computed value=] would be a color other than a [=system color=],
-	it must instead compute to an appropriate [=system color=],
-	as chosen by the user agent.
-
-	For this purpose, any color value with the capability of "fallback" to another color,
-	such as the ''color()'' function,
-	must be allowed to fall back to a system color if specified.
-
-	The "appropriate system color" for 'background-color'
-	must be matched to 'color':
-	if 'color' is a [=system color=],
-	'background-color' must be the opposite color
-	from the [=system color pairings=]
-	(taking ''canvastext'' if 'color' is ''canvas'',
-	and ''canvas'' if 'color' is ''graytext'').
-	It must also take its alpha channel from the original 'background-color' [=computed value=].
-
-	Additionally, 'box-shadow' and 'text-shadow' must be reset to ''box-shadow/none''.
-	'background-image' is reset to ''background-image/none'' unless the original value is a ''url()'' function.
-
-	'color-scheme' on the element must compute to ''light dark'',
-	to allow the user preference (see [[#forced|above]])
-	to be respected.
+	if its [=computed value=] would be a color other than a [=system color=],
+	it is instead forced to a [=system color=] as follows:
+
+	* If the color value indicates a “fallback” color
+		(as in the ''color()'' function in [[CSS-COLOR-5]])
+		and that fallback color is a [=system color=],
+		then the color is forced to that [=system color=].
+	* Else for 'background-color' in particular,
+		it is forced to
+		the color opposite the 'color' property’s [=system color=] value
+		in the [=system color pairings=],
+		using ''CanvasText'' as the opposite of ''Canvas''.
+		However, its alpha channel is taken from
+		the original 'background-color' value
+		so that transparent backgrounds remain transparent.
+	* In all other cases, the UA determines
+		the appropriate forced [=system color=]--
+		which should match the color that would result
+		from an empty [=author style sheet=]
+		whenever all of the element’s affected properties
+		are likewise UA-determined.
+
+	Additionally:
+	* 'box-shadow' and 'text-shadow' compute to to ''box-shadow/none''
+	* 'background-image' computes to ''background-image/none''
+		unless the original value contains a ''url()'' function
+	* 'color-scheme' computes to ''light dark''
 
 	UAs may further tweak these <a>forced colors mode</a> heuristics
 	to provide better user experience.