[mediaqueries-5] Editorial cleanup of prefers-color-scheme: Fix copy-paste error; s/system|interface/page/g; define what light/dark theme means.

Author: fantasai

mediaqueries-5/Overview.bs

@@ -600,7 +600,7 @@ Detecting the desire for increased or decreased color contrast from elements on
 	page to try to undo what the system might be enforcing.
 
 <h3 id="prefers-color-scheme">
-Detecting the desire for increased or decreased color contrast from elements on the page: the 'prefers-color-scheme' feature</h3>
+Detecting the desire for light or dark color schemes: the 'prefers-color-scheme' feature</h3>
 
 	<pre class='descdef mq'>
 	Name: prefers-color-scheme
@@ -610,7 +610,7 @@ Detecting the desire for increased or decreased color contrast from elements on
 	</pre>
 
 	The 'prefers-color-scheme' media feature is used to detect if the user
-	has requested the system use a light or dark color theme.
+	has requested the page use a light or dark color theme.
 
 	<dl dfn-type=value dfn-for="@media/prefers-color-scheme">
 		<dt><dfn>no-preference</dfn>
@@ -622,12 +622,12 @@ Detecting the desire for increased or decreased color contrast from elements on
 		<dt><dfn>light</dfn>
 		<dd>
 			Indicates that user has notified the system that they
-			prefer an interface that has a light theme.
+			prefer a page that has a light theme (dark text on light background).
 
 		<dt><dfn>dark</dfn>
 		<dd>
 			Indicates that user has notified the system that they
-			prefer an interface that has a dark theme.
+			prefer a page that has a dark theme (light text on dark background).
 
 	</dl>