fixed the background issue on the tasks tab

app/templates/editor/level/tasks-tab.jade

@@ -1,4 +1,6 @@
-mixin task-row(cid)
+.nano.editor-nano-container
+  .nano-content
+    mixin task-row(cid)
       - var task = view.getTaskByCID(cid)
       - var taskName = task.get('name');
       - var isComplete = task.get('complete')
@@ -21,7 +23,7 @@ mixin task-row(cid)
             else
               span= taskName
 
-block
+    block
       table.table.table-striped.table-hover
         tr
           th.task-check Complete