/* A black handoff between documents mounted in the same browsing context. */
.hub { transition: opacity 650ms cubic-bezier(.4,0,.2,1); }
body.hub-leaving .hub { opacity: 0; pointer-events: none; }
body[data-hub-arrival] #twin-world { opacity: 1; transition: opacity 1000ms cubic-bezier(.4,0,.2,1); }
body[data-hub-arrival="loading"] #twin-world { opacity: 0; pointer-events: none; }
@media (prefers-reduced-motion: reduce) {
  .hub, body[data-hub-arrival] #twin-world { transition: none; }
}