[css-scrollbars-1] Fix a typo.

Author: upsuper

css-scrollbars-1/Overview.bs

@@ -51,7 +51,7 @@ Values</h3>
   For readability they have not been repeated explicitly.
 
 <h2 id="scrollbar-color-properties">
-Scrollbar Colors: the 'scrollbar-face-color' and 'scrollbar-track-color' properties/h2>
+Scrollbar Colors: the 'scrollbar-face-color' and 'scrollbar-track-color' properties</h2>
 
 <pre class="propdef">
 Name: scrollbar-face-color,