Modal

<button class="btn btn-primary" type="button" data-toggle="modal" data-target="#exampleModalOne">
    Open simple modal (popup)
  </button>
  <!-- Modal -->
<div class="modal modal-popup fade" id="exampleModalOne" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
  <div class="modal-dialog">
    <div class="modal-content">
      <div class="modal-header">
        <h4 class="modal-title" id="exampleModalLabel">Modal title</h4>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">&times;</span>
        </button>
      </div>
      <div class="modal-body padding-responsive">
        <p>A congue consectetur ullamcorper vestibulum hac malesuada cras ante tortor donec leo parturient fames suspendisse tristique.Parturient fames lectus urna in venenatis cum a feugiat a mus justo a cursus sem ut id nullam vulputate.Interdum sem integer egestas tellus a sem hac.</p>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-ghost-dark-gray mdi mdi-close" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary mdi mdi-check-bold">Save changes</button>
      </div>
    </div>
  </div>
</div>

ex: Popup Danger

      <div class="modal-header bg-danger">

ex: Popup XL

      <div class="modal-dialog modal-xl">
      <div class="modal-dialog modal-lg">
      <div class="modal-dialog modal-sm">

another name is Slide panel

stacked popups