[css-borders-4] fix caption

Author: tabatkins

css-borders-4/Overview.bs

@@ -529,7 +529,7 @@ The 'corner-shape' Shorthand</h4>
 		<figure>
 			<img src="images/superellipse-param.svg" width="480" height="360">
 			<figcaption>
-				Rendering examples of different ''superellipse()'' values.
+				Different ''superellipse()'' values for the top right corner: infinity, 1, 0, -1, and -infinity.
 			</figcaption>
 		</figure>
 	</div>