how do I set Top margin of Print

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C#

ASP.NET

Dear Sir,

I am using Java Script to print. It is ...

function printPartOfPage(elementId)
    {
     var printContent = document.getElementById(elementId);
     var windowUrl = 'about:blank';
     var uniqueName = new Date();
     var windowName = 'Print' + uniqueName.getTime();
     var printWindow = window.open(windowUrl, windowName,
    'left=0,top=0,width=725,height=950');

     printWindow.document.write(printContent.innerHTML);
     printWindow.document.close();
     printWindow.focus();
     printWindow.print();
     printWindow.close();
    }

I require to set Top Margin. Please suggest how do I set margin.