[css-ui-4] Markup fix

Author: frivoal

css-ui-4/Overview.bs

@@ -1745,7 +1745,7 @@ without adverse consequences to compatibility,
 so this specification allows flexibility.
 
 
-<h2 id="styling-widgets" oldids="form-styling control-styling">Styling Widgets</h2>
+<h2 id="styling-widgets" oldids="form-styling, control-styling">Styling Widgets</h2>
 
 <h3 id="appearance-switching" caniuse="css-appearance">Switching appearance</h3>