Как выровнять значок по центру внутри кнопки?

.close-button button {
  border: 1px solid black;
  border-radius: 50%;
  height: 25px;
  width: 25px;
  outline: none;
}

.close-button {
  margin-right: 50%;
  margin-top: 7%;
  /*  I wrote to center the button */
}

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/css/bootstrap.min.css" integrity="sha384-Smlep5jCw/wG7hdkwQ/Z5nLIefveQRIY9nfy6xoR1uRYBtpZgI6339F5dgvm/e9B" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/js/bootstrap.min.js" integrity="sha384-o+RDsa0aLu++PJvFqy8fFScvbHFLtbvScb8AjopnFD+iEQ7wo/CG0xlczd+2O/em" crossorigin="anonymous"></script>

<button type="button" data-toggle="modal" data-target="#exampleModal" class="btn btn-success">Click</button>

<div class="modal" id="exampleModal">
  <div class="modal-dialog">
    <div class="modal-content" style="height:100px;">
      <div class="close-button">
        <button type="button" class="close" data-dismiss="modal">×</button>
      </div>
    </div>
  </div>
</div>

https://www.w3schools.com/code/tryit.asp?filename=FTCZIK9F0A66

Text-align:center or line-height:50% not working. How can fix it ? Thank you.