[scroll-animations-1] Fix markup

Author: fantasai

scroll-animations-1/Overview.bs

@@ -865,7 +865,7 @@ spec: cssom-view-1; type: dfn;
 	to <a href="https://www.w3.org/TR/css-animations/">CSS Animations</a>
 	and <a href="https://www.w3.org/TR/web-animations/">Web Animations</a>.
 
-## Named Timeline Ranges ##
+## Named Timeline Ranges ## {#named-ranges}
 
 	A <dfn export>named timeline range</dfn>
 	is a named segment of an animation [=timeline=].