Vertical-alignment text in Bootstrap's List Group

I've tried to vertical align text in Bootstrap's list group (inside of tag li) with display: table-cell; line-height: 50px; vertical-align: middle;, but it doesn't work at all. Help me with it, please. ;)

<div class="row">
                <div class="col-md-12">
                    <ul class="list-group">


                    <li class="list-group-item clearfix">Byl jsi pořádně prošťouchán uživatelem <strong>hakys</strong>.
                                <form action="my_pokes.php" method="post">
                                    <span class="pull-right">
                                        <button class="btn btn-success" name="poke_hakys">Šťouchnout zpět</button>&nbsp;
                                        <button class="btn btn-danger" name="delete_hakys">Smazat šťouchnutí</button>
                                    </span>
                                </form>
                            </li>                        </ul>
                </div>
            </div>