How can I hide an element in an iframe?

I tried to add an iframe element (ID is "intra"), wich works very well.

But the next thing I tried was hiding a div (id="top") to hide the header from: is there a way hide elements in IFRAME src page?, but this wouldn't remove the header.

Here's my code:

    <script src="https://code.jquery.com/jquery-1.11.1.min.js"></script>

    <script type="text/javascript">
    $('#intra').load(function(){
        $('#intra').contents().find('#top').hide();
    });

Can you guys see what's wrong with this?

Or is there even a possibility to hide that element using HTML?