Selecting a tag that is not present in the HTML.

[wondersavant]

https://btholt.github.io/complete-intro-to-web-dev-v3/lessons/css/pseudoclasses-and-pseudoelements
Pseudoelements

<div class="chapter">This is a chapter of my book.</div>

<div class="chapter">This is a second chapter of my book.</div>

<style>
  .chapter p {
    margin: 0;
  }
  .chapter::after {
    content: "❦";
    font-size: 50px;
    text-align: center;
    display: block;
  }
</style>

there are no p tags within those elements in the given HTML