CSS selector for details element when opened

Question

Is there a CSS selector (like a pseudo class) that can target the details element when it is open?

One possible use for this would be to change the color of the summary element when the user open the details element.

Answer 1

Use the attribute [open] selector

details summary {
  background: pink;
}

details {
  background: lightgreen;
}

details[open] summary {
  background: red;
}

<details>
  <summary>Details</summary>
  Lorem ipsum, dolor sit amet consectetur adipisicing elit. Fuga, incidunt dolores! Laudantium fugit aspernatur rem autem, expedita ut id necessitatibus, perferendis, accusantium esse repudiandae?
</details>