我有用于打印div内容的此javascript代码。将css写入javascript代码does not work

function PrintElem() 
{ 
    var mywindow = window.open('', 'PRINT', 'height=600,width=800'); 

    mywindow.document.write(''); 

    mywindow.document.write(''); 

    mywindow.document.write(''); 
    mywindow.document.write('
' + document.title + '
'); 
    mywindow.document.write(document.getElementById("favorite_items").innerHTML); 
    mywindow.document.write(''); 

    mywindow.document.close(); // necessary for IE >= 10 
    mywindow.focus(); // necessary for IE >= 10*/ 

    mywindow.print(); 
    mywindow.close(); 

    return true; 
} 

我该怎么写一些打印CSS的新窗口，JavaScript打开？