basic theme: Add a "clearer" at the end of the "body".

sphinx/themes/basic/layout.html

@@ -181,6 +181,7 @@
       {%- endif %}
           <div class="body" role="main">
             {% block body %} {% endblock %}
+            <div class="clearer"></div>
           </div>
       {%- if render_sidebar %}
         </div>