[css-color-5] Fix syntax highlighting in example, see #8499

Author: svgeesus

css-color-5/Overview.bs

@@ -982,7 +982,7 @@ so it has meaningful values for the channels.</p>
 		to account for the changed position.
 		For example,</p>
 
-	<pre>
+	<pre  highlight=css>
 		color: color(from color(srgb 0 0 0 / 60%) srgb alpha 0.6 0.6 / 0.9);
 	</pre>
 
@@ -996,7 +996,7 @@ so it has meaningful values for the channels.</p>
 		legacy rgb() syntax:
 	</p>
 
-	<pre>
+	<pre  highlight=css>
 		color: rgb(from rgb(0 0 0 / 60%) alpha 153 153 / 0.9);
 	</pre>