# Pastebin 3PIUwxZd
.a, :root:at(layer b) {
  .c, :root:at(layer d) {
    /* declarations */
  }
}

/* explodes into: */

.a {
  .c { /* declarations */ }
  @layer d {
    :root { /* declarations */ }
  }
}
@layer b {
  .c { /* declarations */ }
  @layer d {
    :root { /* declarations */ }
  }
}