/* ==========================================================================
   Income Outsource — Back to Top Button
   Fixed bottom-right control, hidden until the page has scrolled past a
   threshold. Solid "ledger ink" stamp (matches footer/code-block/pagination
   treatment) so it stays dark in both themes — see CLAUDE.md's Astra
   theming notes on --color-ink vs --color-primary.
   ========================================================================== */

.back-to-top {
  position: fixed;
  right: var(--space-5);
  bottom: var(--space-5);
  z-index: var(--z-back-to-top);

  display: flex;
  align-items: center;
  justify-content: center;
  width: 3rem;
  height: 3rem;
  padding: 0;
  border: none;
  border-radius: var(--radius-pill);

  background: var(--color-ink);
  color: var(--color-on-ink);
  box-shadow: var(--shadow-md);

  opacity: 0;
  visibility: hidden;
  transform: translateY(0.5rem) scale(0.9);
  transition:
    opacity var(--duration-base) var(--ease-standard),
    transform var(--duration-base) var(--ease-standard),
    visibility 0s linear var(--duration-base),
    box-shadow var(--duration-fast) var(--ease-standard),
    background-color var(--duration-fast) var(--ease-standard);
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0) scale(1);
  transition:
    opacity var(--duration-base) var(--ease-standard),
    transform var(--duration-base) var(--ease-standard),
    visibility 0s linear 0s,
    box-shadow var(--duration-fast) var(--ease-standard),
    background-color var(--duration-fast) var(--ease-standard);
}

.back-to-top:hover,
.back-to-top:focus-visible {
  background: var(--color-ink-light);
  box-shadow: var(--shadow-lg);
  transform: translateY(-0.15rem) scale(1.04);
}

.back-to-top.is-visible:hover,
.back-to-top.is-visible:focus-visible {
  transform: translateY(-0.15rem) scale(1.04);
}

.back-to-top:active {
  transform: translateY(0) scale(0.97);
}

.back-to-top:focus-visible {
  outline: none;
  box-shadow: var(--shadow-lg), var(--shadow-focus);
}

.back-to-top__icon {
  width: 1.25rem;
  height: 1.25rem;
  flex-shrink: 0;
  stroke: currentColor;
}

@media (max-width: 600px) {
  .back-to-top {
    width: 2.75rem;
    height: 2.75rem;
    right: var(--space-4);
    bottom: var(--space-4);
  }

  .back-to-top__icon {
    width: 1.125rem;
    height: 1.125rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .back-to-top {
    transition: opacity var(--duration-fast) linear, visibility 0s linear;
  }
}