Make the sidebar close a button and add aria-label to it

client/views/chan.tpl

@@ -1,7 +1,7 @@
 {{#each channels}}
 <div data-id="{{id}}" data-target="#chan-{{id}}" data-title="{{name}}" class="chan {{type}}">
 	<span class="badge{{#if highlight}} highlight{{/if}}" data-count="{{unread}}">{{#if unread}}{{unread}}{{/if}}</span>
-	<span class="close"></span>
+	<button class="close" aria-label="Close"></button>
 	<span class="name" title="{{name}}">{{name}}</span>
 </div>
 {{/each}}