.voltar-topo{
  position:fixed;
  right:24px;
  bottom:24px;
  width:52px;
  height:52px;
  border-radius:50%;
  background:var(--cor-principal,#1b7cff);
  color:#fff;
  display:flex;
  align-items:center;
  justify-content:center;
  text-decoration:none;
  box-shadow:0 10px 25px rgba(0,0,0,.25);
  z-index:99999;
  opacity:0;
  transform:translateY(12px);
  pointer-events:none;
  transition:opacity .2s ease, transform .2s ease;
}
.voltar-topo.show{
  opacity:1;
  transform:translateY(0);
  pointer-events:auto;
}
.voltar-topo svg{display:block}