[css-color-adjust-1] Forced backgrounds should not affect alpha. w3c#4175

Author: fantasai

css-color-adjust-1/Overview.bs

@@ -349,7 +349,9 @@ 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),
-	the following <a>user origin</a> declarations [[!CSS-CASCADE-4]]
+	colors must be force-adjusted to the user’s preferred color palette.
+
+	The following <a>user origin</a> declarations [[!CSS-CASCADE-4]]
 	are applied to the element:
 
 	<pre>
@@ -358,7 +360,6 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		stroke: revert !important;
 		text-decoration-color: revert !important;
 		text-emphasis-color: revert !important;
-		background-color: revert !important;
 		border-color: revert !important;
 		outline-color: revert !important;
 		column-rule-color: revert !important;
@@ -369,6 +370,16 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		text-shadow: none !important;
 	</pre>
 
+	For elements that have a background specified in the UA style sheet,
+	the background color is forced via:
+	<pre>
+		background-color: revert !important;
+	</pre>
+
+	Whereas for all other elements, the 'background-color' is instead adjusted
+	by forcing all channels other than alpha
+	to match ''Canvas''.
+
 	Additionally, on <em>on user input controls (except button-like controls) only</em>:
 	<pre>
 		background-image: none !important;