[css-color-4][editorial] move specific opacity tests to closest relevant portion of the spec

Author: svgeesus

css-color-4/Overview.bs

@@ -4400,11 +4400,9 @@ Transparency: the 'opacity' property</h2>
 	</pre>
 
 	<wpt>
-		opacity-overlapping-letters.html
 		parsing/opacity-computed.html
 		parsing/opacity-valid.html
 		parsing/opacity-invalid.html
-		body-opacity-0-to-1-stacking-context.html
 	</wpt>
 
 	<dl>
@@ -4434,6 +4432,10 @@ Transparency: the 'opacity' property</h2>
 	are treated <em>as a whole</em>;
 	any overlapping portions do not increase the opacity.
 
+	<wpt>
+		opacity-overlapping-letters.html
+	</wpt>
+
 	<figure id="arabic-opacity-rendering">
 		<img src="images/joining-and-transparency.svg" width=713 height=156
 		alt="overlapping glyphs rendered correctly, and incorrectly">
@@ -4454,6 +4456,10 @@ Transparency: the 'opacity' property</h2>
 	(This prevents its contents from interleaving in the z-axis
 	with content outside it.)
 
+	<wpt>
+		body-opacity-0-to-1-stacking-context.html
+	</wpt>
+
 	Furthermore, if the 'z-index' property applies to the box,
 	the ''z-index/auto'' value is treated as ''0'' for the element;
 	it is otherwise painted on the same layer within its parent stacking context