EasyUI treegrid customize header text

I am trying to center a header text in the above control:

 var td = $(elem).treegrid('getPanel').find('div.datagrid-header td[field="alarms"]');
        td.css('text-align', 'center');
        td.css('height', '40');

The height gets changed to 40, but the text is not aligning.What might the problem be?

Thanks