/* nav-scroll.css — owned by Agent A (Tier 1).
   Reading-progress hairline, back-to-top pill.
   Section indicator styles live in layout.css (Tier 0) and are not duplicated here. */

/* ── Reading progress hairline ─────────────────────────────────────────────── */

.nav-reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--accent);
  transform: scaleX(0);
  transform-origin: 0 50%;
  z-index: 100;
  pointer-events: none;
  will-change: transform;
  transition: transform 80ms linear;
}

@media (prefers-reduced-motion: reduce) {
  .nav-reading-progress { transition: none; }
}

/* ── Back-to-top pill ──────────────────────────────────────────────────────── */

.nav-back-to-top {
  position: fixed;
  right: max(var(--s-4), env(safe-area-inset-right, 0));
  bottom: max(var(--s-5), env(safe-area-inset-bottom, 0));
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--surface-0);
  color: var(--text);
  border: 1px solid var(--border-strong);
  font-size: 18px;
  font-weight: 600;
  cursor: pointer;
  box-shadow: 0 4px 16px var(--shadow);
  opacity: 0;
  transform: translateY(8px);
  transition: opacity var(--dur-med) var(--ease), transform var(--dur-med) var(--ease), background var(--dur) var(--ease);
  z-index: 50;
}

.nav-back-to-top[data-visible="true"] {
  opacity: 1;
  transform: translateY(0);
}

.nav-back-to-top:hover {
  background: var(--surface-1);
}

.nav-back-to-top:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  .nav-back-to-top { transition: none; }
}