/* The persistent shell's navigation (D179): the rail stays put while the page region cross-fades, a thin bar shows
   only for a slow navigation, and the new page's heading takes the focus without a ring. */

.rail { view-transition-name: rail; }
::view-transition-group(*),
::view-transition-old(*),
::view-transition-new(*) { animation-duration: 120ms; }
@media (prefers-reduced-motion: reduce) {
  ::view-transition-group(*),
  ::view-transition-old(*),
  ::view-transition-new(*) { animation: none; }
}

.shell-progress {
  position: fixed;
  z-index: 100;
  inset: 0 0 auto;
  height: 2px;
  background: var(--st-accent);
  opacity: 0;
  pointer-events: none;
  transform: scaleX(0);
  transform-origin: left;
  view-transition-name: shell-progress;
}
.shell-progress[data-on] {
  opacity: 1;
  transform: scaleX(0.8);
  transition: transform 2s cubic-bezier(0.1, 0.6, 0.2, 1), opacity 0.1s;
}