details {
  border: 1px solid black;
  padding: 1rem;

  &[open] {
    background: red;
    color: white;

    summary {
      margin-block-end: 0.5rem;
    }
  }

  body:has(&[open]) {
     background: pink;

     .something-else {
       translate: 0 0;
     }
  }
}

.something-else {
  position: absolute;
  bottom: 20px;
  left: 20px;
  translate: 0 100px;
  transition: 0.2s;
  font: 800 50px system-ui;
}

body {
  overflow: clip;
}