.back-to-top {
  position: fixed;
  right: clamp(16px, 2.5vw, 34px);
  bottom: clamp(18px, 4vw, 38px);
  z-index: 40;
  width: 48px;
  height: 48px;
  display: grid;
  place-items: center;
  border: 1px solid rgba(255, 250, 241, 0.7);
  border-radius: 50%;
  background: rgba(48, 44, 66, 0.92);
  box-shadow: 0 8px 24px rgba(20, 15, 29, 0.2);
  color: #fffaf1;
  cursor: pointer;
  font: 600 1.25rem/1 Georgia, serif;
  opacity: 0;
  transform: translateY(12px);
  pointer-events: none;
  transition: opacity 180ms ease, transform 180ms ease, background 180ms ease;
}

.back-to-top.is-visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}

.back-to-top:hover { background: #9a6639; }
.back-to-top:focus-visible { outline: 3px solid #f3c879; outline-offset: 3px; }

@media (max-width: 780px) {
  .back-to-top { width: 44px; height: 44px; right: 14px; bottom: 18px; }
}