Add padding around courseware content

cms/static/sass/_base.scss

@@ -171,6 +171,10 @@ label {
 //
 // -------------------------------------
 
+.edit-pane {
+    padding: 40px;
+}
+
 .xmodule_display {
     font-size: 16px;
 }

cms/templates/unit.html

@@ -12,7 +12,9 @@
             <li><span class="current-page">S3V2: Properties of Linearity</span></li>
           </ul>
         </nav>
+        <section class='edit-pane'>
           ${editable_preview}
+        </section>
       </article>
 
       <div class="sidebar">