#backToTop {
  position: fixed;
  bottom: calc(20px + env(safe-area-inset-bottom));
  right: 20px;
  width: 48px; height: 48px;
  border: none; border-radius: 50%;
  background: #99ddcc; color: #000;
  display: flex; align-items: center; justify-content: center;
  opacity: 0; pointer-events: none;
  transition: opacity .3s, transform .3s;
  box-shadow: 0 4px 10px rgba(0,0,0,.2);
  z-index: 99999;
}
#backToTop:hover { background:#77c9b6; transform: translateY(-2px); }
#backToTop svg { width:22px; height:22px; fill: currentColor; }

/* While scrolling: give the arrow a gentle lift loop */
#backToTop.is-animating svg {
  animation: btt-lift 0.8s ease-in-out infinite;
}
@keyframes btt-lift {
  0%   { transform: translateY(0); }
  50%  { transform: translateY(-3px); }
  100% { transform: translateY(0); }
}