To custom the panel tools, you have to define it inside an existing element. Please try this:
<div class="easyui-panel" title="Custom Panel Tools" style="width:700px;height:200px;" data-options="closable:true,tools:'#tt'">
</div>
<div id="tt">
<span class="icon-transparent" style="display:inline-block;width:16px;height:16px;vertical-align:top"></span>
</div>