bootstrap: content center

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="container-fluid">
    <!-- START FORM -->
    <form method="post" class="form-horizontal"> 
        <!-- ROW 1 CHECKBOXES -->
<div class='row'>
                <div class='col-md-4'>
                    <div class='col-md-2'><input type='checkbox' class='form-control chk_boxes2' name='check_list[]'></div>
                    <label class='col-md-2'>Medewerker</label>        
                </div>
                <div class='col-md-4'> 
                    <div class='col-md-2'><input type='checkbox' class='form-control chk_boxes2' name='check_list[]'></div> 
                    <label class='col-md-2'>Medewerker</label>
                </div>
                <div class='col-md-4'>
                    <div class='col-md-2'><input type='checkbox' class='form-control chk_boxes2' name='check_list[]'></div>
                    <label class='col-md-2'>Medewerker</label>
                </div>
                </div>
          
        <!-- ROW SUBMIT -->
        <div class="row down right">
            <div class="col-md-6">
                <label class="col-md-3">Check all</label>
                <div class="col-md-3"><input type='checkbox' class="chk_boxes form-control">
            </div>
            <div class="col-md-6">
                <input type="submit" name="Verder" value="Verder" class="form-control btn-primary">
            </div>
        </div>  
    </form>
    <!-- END FORM -->
</div>

CSS

.form-horizontal{
  text-align: center;
}

JavaScript

$('.down').css('margin-top', function () {
    return ($(window).height() - $(this).height()) / 2.8
});

/*$('.right').css('margin-left', function () {
    return ($(window).height() - $(this).height()) / 2
});*/