在Bootstrap 4中，Toast是不可见的，并且无法关闭

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.6.0/dist/css/bootstrap.min.css">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@4.6.0/dist/js/bootstrap.min.js"></script>

<div id="myToast" class="toast" role="alert" aria-live="assertive" aria-atomic="true" data-delay="5000">
  <div class="toast-header">
    <strong class="mr-auto">Toast标题</strong>
    <button type="button" class="ml-2 mb-1 close" data-dismiss="toast" aria-label="Close">
      <span aria-hidden="true">&times;</span>
    </button>
  </div>
  <div class="toast-body">
    Toast内容
  </div>
</div>

var toast = document.getElementById('myToast');
var toastInstance = new bootstrap.Toast(toast);
toastInstance.show();