[css-images-4] Use the correct % in example. Fixes w3c#3123.

Author: tabatkins

css-images-4/Overview.bs

@@ -1215,7 +1215,7 @@ Conic Gradient Examples</h4>
 
 		<pre class=lang-css>
 			background: conic-gradient(from 45deg, white, black, white);
-			background: conic-gradient(hsl(0,0%,87.5%), white 45deg, black 225deg, hsl(0,0%,87.5%));
+			background: conic-gradient(hsl(0,0%,75%), white 45deg, black 225deg, hsl(0,0%,75%));
 		</pre>
 
 		<img src="images/conic3.png" alt="" >