[css-scoping] Whoops, put an id in there.

Author: tabatkins

css-scoping/Overview.bs

@@ -242,7 +242,7 @@ Selecting Outside the Scope: '':scope-context()'' pseudo-class</h4>
 ████████  ████████ ██       ██     ██  ███████  ████████    ██
 -->
 
-<h2 id=''>
+<h2 id='default-element-styles'>
 Default Styles for Custom Elements</h2>
 
 	When defining <a>custom elements</a>,