/* ==========================================================================
   back-to-top — fixed button, shown past 900px of scroll
   ========================================================================== */

.back-to-top {
  position: fixed;
  right: 22px;
  bottom: 22px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--charcoal);
  border: 1px solid var(--line);
  color: var(--sand);
  font-size: 18px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  z-index: 60;
  opacity: 0;
  pointer-events: none;
  transform: translateY(10px);
  transition: opacity 0.3s ease, transform 0.3s ease, background 0.2s ease;
}
.back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}
.back-to-top:hover {
  background: var(--rust);
}