

.container::after {
  display: block;
  content: "after";
  background: yellow;
  grid-area: 3 / 1;
}

details {
  display: grid;
  grid-template: subgrid / subgrid;
  grid-area: 2 / 2 / 4 / 4;
}

details[open]::details-content {
  /* continue testing the old behavior that this was written to test */
  display: contents;
}

summary {
  display: block;
  background: fuchsia;
  grid-area: 1 / 1;
}

.contents {
  background: silver;
  grid-area: 2 / 2;
}

</style>

<div class="container">
  <details open>
  