<!DOCTYPE html>
<style>
  html {
    overflow: hidden;
  }

  dialog {
    container-type: size;
    width: 100px;
    height: 100px;
  }

  @container (width > 1px) {
    dialog::backdrop {
      margin: 10px;
      background-color: green;
    }
  }
</style>
<dialog id=dialog>
  Hello World
</dialog>
<script>
  dialog.showModal();
</script>
