.back-to-top{
  position:fixed;
  right:18px;
  bottom:72px;
  z-index:890;
  display:grid;
  place-items:center;
  width:44px;
  height:44px;
  padding:0;
  border:1px solid rgba(20,20,20,.16);
  border-radius:999px;
  background:#fff;
  color:#171717;
  box-shadow:0 8px 24px rgba(0,0,0,.14);
  font:900 20px/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  cursor:pointer;
  opacity:0;
  visibility:hidden;
  pointer-events:none;
  transform:translateY(8px);
  transition:opacity .18s ease,visibility .18s ease,transform .18s ease,box-shadow .18s ease;
}
.back-to-top.is-visible{
  opacity:1;
  visibility:visible;
  pointer-events:auto;
  transform:translateY(0);
}
.back-to-top:hover{
  transform:translateY(-2px);
  box-shadow:0 10px 28px rgba(0,0,0,.18);
}
.back-to-top:focus-visible{
  outline:3px solid var(--blue);
  outline-offset:2px;
}
@media (prefers-reduced-motion:reduce){
  .back-to-top{transition:none}
}
@media (max-width:720px){
  .back-to-top{
    right:12px;
    bottom:calc(128px + env(safe-area-inset-bottom));
  }
}