/* ============================================================================
   Small shared UI widgets that don't belong in css/styles.css (1yr immutable
   cache — any edit there needs a ?v= bump across every referencing page).
   New, uncached-so-far file: safe to add without touching styles.css/main.js.
   ============================================================================ */
.back-to-top-btn {
  position: fixed;
  bottom: 24px;
  inset-inline-end: 24px;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  border: none;
  background: var(--sky-dark, #0ea5e9);
  color: #fff;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 14px rgba(14, 165, 233, 0.35);
  cursor: pointer;
  z-index: 900;
  opacity: 0;
  pointer-events: none;
  transform: translateY(8px);
  transition: opacity 0.2s ease, transform 0.2s ease;
}
.back-to-top-btn.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}
.back-to-top-btn:hover {
  background: var(--sky-darker, #0284c7);
}
@media (max-width: 480px) {
  .back-to-top-btn { bottom: 16px; inset-inline-end: 16px; width: 42px; height: 42px; }
}