Native modals

Cómo usar los modales nativos de HTML5, sin javascript.

HTML 
<div class="content">
  <button popovertarget="modal">modal</button>

  <div id="modal" popover>
    <h2>Modal Box</h2>
    <p>This is a modal box.</p>
    <button popovertarget="modal">close</button>
  </div>
</div>