How to remove rel stylesheet attribute or modify it's effect from external iframe?

Question

So here is the iframe:

<iframe src="http://example.com/example.php"></iframe>

and the output of it

<link rel='stylesheet' href="http://example.com/css/style.css" type='text/css' />


<div id="someid" class="someclass">
some random text....
</div>

Now how can i control this html div given that i don't own example.com?

How can i add css from my website to modify this div?

I've tried this but it doesn't work:

<script>
$('iframe').load( function() {
    $('iframe').contents().find("head")
      .append($("<style type='text/css'>  .header{display:none;}  </style>"));
});
</script>