None of the solutions above work perfectly.They either loses CSS or have to include/edit external CSS file. I found a perfect solution that will not lose your CSS nor you have to edit/add external CSS.
HTML:
<div id='printarea'>
<p>This is a sample text for printing purpose.</p>
<input type='button' id='btn' value='Print' onclick='printFunc();'>
</div>
<p>Do not print.</p
JQuery:
function printFunc() {
var divToPrint = document.getElementById('printarea');
var htmlToPrint = '' +
'<style type="text/css">' +
'table th, table td {' +
'border:1px solid #000;' +
'padding;0.5em;' +
'}' +
'</style>';
htmlToPrint += divToPrint.outerHTML;
newWin = window.open("");
newWin.document.write("<h3 align='center'>Print Page</h3>");
newWin.document.write(htmlToPrint);
newWin.print();
newWin.close();
}