tests/visual/containing-block.html

<!DOCTYPE html> <title>Basic Visual Test</title>

<style>
  @import '/reset.css';
  #reference {
    width: 200px;
    height: 200px;
    background-color: red;
    box-shadow: inset 0 0 0 1px black;
  }

  #popper {
    width: 100px;
    height: 100px;
    background-color: rebeccapurple;
    box-shadow: inset 0 0 0 1px black;
  }

  #containing-block {
    background: gray;
    width: 400px;
    height: 400px;
    overflow: auto;
    will-change: transform;
  }

  #containing-block::before {
    content: '';
    display: block;
    height: 200px;
    width: 1px;
  }

  #containing-block::after {
    content: '';
    display: block;
    height: 200px;
    width: 1px;
  }
</style>

<div id="containing-block">
  <div id="reference">Reference Box</div>
  <div id="popper">Popper Box</div>
</div>

<script type="module">
  import { createPopper } from './dist/popper.js';
  const reference = document.querySelector('#reference');
  const popper = document.querySelector('#popper');

  window.instance = createPopper(reference, popper, {
    strategy: 'fixed',
  });
</script>