[css-pseudo-4] Fix link

Author: fantasai

css-pseudo-4/Overview.bs

@@ -198,7 +198,8 @@ Styling the ''::first-line'' Pseudo-element</h4>
   </ul>
 
   Setting 'line-height' on ''::first-line'' affects
-  the fragment of the [=root inline=] that wraps the contents of the first line,
+  the fragment of the [=root inline box=]
+  that wraps the contents of the first line,
   and therefore can both increase and decrease the height of the first line box.
   <!-- Issue 2282 -->