Update docs.html

vanilla/templates/_layouts/docs.html

@@ -63,7 +63,7 @@
                 {% for item in sideNavigation %}
 
                   <li class="p-side-navigation__item">
-                    <button class="p-side-navigation__accordion-button" aria-expanded="false">{{ item.heading | replace("{version}", version) }}</button>
+                    <h3 class="p-side-navigation__heading">{{ item.heading | replace("{version}", version) }}</h3>
                     <ul class="p-side-navigation__list">
                       {% for subheading in item.subheadings %}
                       {{ side_nav_item(subheading.url, subheading.title) }}