[css-pseudo-4][editorial] Improve term linking

Author: fantasai

css-pseudo-4/Overview.bs

@@ -175,7 +175,7 @@ Finding the First Formatted Line</h4>
 Styling the ''::first-line'' Pseudo-element</h4>
 
   The ''::first-line'' pseudo-element’s generated box
-  behaves similar to that of an inline-level element, but with certain restrictions.
+  behaves similar to that of an [=inline-level box=], but with certain restrictions.
   The following CSS properties apply to a ''::first-line'' pseudo-element:
   <ul>
     <li>all font properties (see [[CSS-FONTS-3]])