templates/base.html: use a wrapper maxwidth div for nicer margins in the main content

templates/base.html

@@ -34,16 +34,18 @@
       </div>
     </header>
 
-    <main class="maxwidth content">
+    <div class="maxwidth">
+      <main class="content">
         {% block content %}
         {% endblock content %}
       </main>
 
-    <footer class="maxwidth">
+      <footer>
         <p>Copyright {{ now() | date(format="%Y") }} <a href="http://aas.org/">AAS</a>.
           HTML generated with <a href="https://www.getzola.org/">Zola</a>.
           <a href="{{ config.extra.github_url | safe }}">Source code</a>.
         </p>
       </footer>
+    </div>
   </body>
 </html>