.rail {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 10;
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  width: calc(var(--rail-w) + env(safe-area-inset-left));
  height: 100vh;
  height: 100dvh;
  padding: calc(var(--space-3) + env(safe-area-inset-top)) var(--space-1) calc(var(--space-3) + env(safe-area-inset-bottom));
  padding-left: calc(var(--space-1) + env(safe-area-inset-left));
  overflow-y: auto;
  scroll-snap-type: y mandatory;
  scrollbar-width: none;
  background: rgba(11, 12, 16, 0.7);
  background: color-mix(in srgb, var(--bg) 70%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-right: 1px solid var(--line);
}
.rail::-webkit-scrollbar { display: none; }

.pill {
  position: relative;
  z-index: 1;
  flex: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-inline-size: 44px;
  min-block-size: 44px;
  scroll-snap-align: start;
  padding: var(--space-2) var(--space-2);
  border-radius: 999px;
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--fg-muted);
  writing-mode: vertical-rl;
  text-align: center;
  transition: color var(--dur) var(--ease), transform var(--dur) var(--ease);
}
.pill:hover { color: var(--fg); }
.pill:focus-visible { outline-offset: -2px; }
.pill[aria-current="page"] { color: var(--fg); }
.pill:active { transform: scale(0.96); }

.rail__indicator {
  position: absolute;
  top: 0;
  left: 0;
  width: 0;
  height: 0;
  border-radius: 999px;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  transform-origin: top left;
  pointer-events: none;
}
.rail__indicator[data-ready] {
  transition: transform var(--dur) var(--ease), width var(--dur) var(--ease), height var(--dur) var(--ease);
}

@media (min-width: 900px) {
  .rail {
    flex-direction: row;
    width: 100%;
    height: var(--rail-h);
    padding: calc(var(--space-2) + env(safe-area-inset-top)) calc(var(--space-5) + env(safe-area-inset-right)) var(--space-2) calc(var(--space-5) + env(safe-area-inset-left));
    overflow-y: hidden;
    overflow-x: auto;
    scroll-snap-type: none;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }
  .pill {
    writing-mode: horizontal-tb;
    padding: var(--space-2) var(--space-3);
  }
}