[css-images-4] Fixed incorrect example of overlaid radial and conic gradients, w3c#3355

Author: svgeesus

css-images-4/Overview.bs

@@ -1692,7 +1692,7 @@ Conic Gradient Examples</h4>
 		A conic gradient with a radial gradient overlaid on it, to draw a hue & saturation wheel:
 
 		<pre class=lang-css>
-			background: radial-gradient(gray, transparent),
+			background: radial-gradient(closest-side, gray, transparent),
 			            conic-gradient(red, magenta, blue, aqua, lime, yellow, red);
 			border-radius: 50%;
 			width: 200px; height: 200px;