This example shows how to set the width of Dialog to a percentage of its parent container.
<div class="easyui-dialog" title="Fluid Dialog" style="width:80%;height:200px;max-width:800px;padding:10px" data-options="
iconCls:'icon-save',
onResize:function(){
$(this).dialog('center');
}
">
<p>width: 80%; height: 200px</p>
</div>