message: Fix `z-index` bug in `quick-repo-deletion` and `sticky-sidebar`
diff: :root .rgh-quick-repo-deletion[open] span {
  position: relative;
  - z-index: 81;
  + z-index: 91; /* Higher than sticky readme header and `sticky-sidebar` #4192 */
  transform-origin: top;
  }
  :root .rgh-quick-repo-deletion[open] summary::before {
  background-color: var(--color-scale-red-6);
  opacity: 30%;
  + z-index: 91; /* Higher than sticky readme header and `sticky-sidebar` #4192 */
  }
  