Bootstrap modal overflow

Show modal with max height + overflow scroll

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.1.1/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/jasny-bootstrap/3.1.1/css/jasny-bootstrap.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/jasny-bootstrap/3.1.1/js/jasny-bootstrap.js"></script>
<!-- Button trigger modal -->
<button class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal">
  Launch demo modal
</button>

<div class="fixed-header">
    <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
        <h4 class="modal-title">Modal title</h4>
    </div>
</div>

<div id="myModal" class="modal fade">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
                <h4 class="modal-title">Modal title</h4>
            </div>
            <div class="modal-body">
                <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque vel vehicula erat. Phasellus vestibulum leo eu mi tempor blandit. Suspendisse eget iaculis lectus. Donec vitae tempus enim, quis tristique magna. Donec lobortis, sem ac pretium viverra, leo nisl consequat arcu, sit amet ullamcorper nunc turpis ac erat. In rutrum auctor ligula, quis mattis enim lacinia eu. Aliquam at magna a erat laoreet iaculis quis a justo. Donec porttitor vulputate massa, nec suscipit nisi mollis sed.</p>
                <p>Praesent sit amet porttitor magna, auctor feugiat tellus. Sed venenatis tortor turpis, vel vestibulum eros pulvinar et. Pellentesque hendrerit diam quis dui euismod tincidunt. Sed sit amet mauris ipsum. Integer in magna tellus. In tincidunt mi quis nunc gravida sollicitudin. Aliquam ac dui eget erat consequat volutpat in eu...

CSS

.fixed-header {
    z-index: 1100;
    width: 100%;
    position: fixed;
    top: 0;
    left: -8px;
    display: none;
}

.fixed-header .modal-header {
    background-color: #fff;
    width: 598px;
    margin: 0 auto;
}

.affixed {
    display: block;
}

JavaScript

$('#myModal').on('scroll', function() {
    var threshold = 60;

    if ($('#myModal').scrollTop() > threshold) {
        $('.fixed-header').addClass('affixed');
    }
    else {
        $('.fixed-header').removeClass('affixed');
    }
});

$('#myModal').on('hide.bs.modal', function (e) {
    $('.fixed-header').removeClass('affixed');
});

$('.fixed-header button').click(function() {
    $('#myModal').modal('hide');
});