Untitled

<html>
  <title>Some title</title>
  <style type="text/css">
     /* CSS content here */
  </style>
  <body>
    <!-- body content here -->
  </body>
</html>

$("#iframe_constainer")
  .find('iframe:first').contents().find('html:first').html(myHTML);

<div id="iframe_container"><iframe/></div>

<html>
  <html>
    <title>Some title</title>
    <style type="text/css">
       /* CSS content here */
    </style>
    <body>
      <!-- body content here -->
    </body>
  </html>
</html>

document.getElementById("myIframeId").contentWindow.document.write(myHTML);

var iframe = document.getElementById('iframeID');
iframe.contentWindow.document.open();
iframe.contentWindow.document.write(htmlData);
iframe.contentWindow.document.close();