Update index.html

Author: Cornelis G. A. Kolbach

src/pat/collapsible/index.html

@@ -62,7 +62,7 @@ <h3>Click me - I explicitly start out closed and will fade in</h3>
                 nesciunt.
             </p>
         </div>
-        <div class="pat-collapsible closed"
+        <div class="pat-well pat-collapsible closed"
              id="load-on-open"
              data-pat-collapsible="load-content: /code/src/pat/collapsible/collapsible-sources.html#panel1; close-trigger: #close; open-trigger: #open">
             <h3>Click me! - I will load my content when opened</h3>