.back-to-top {
  position:fixed;
  right:24px;
  bottom:24px;
  z-index:20;
  display:grid;
  place-items:center;
  width:46px;
  height:46px;
  border:2px solid #fff;
  border-radius:50%;
  background:#002459;
  color:#fff;
  font-size:24px;
  font-weight:800;
  line-height:1;
  box-shadow:0 7px 18px rgba(0,36,89,.25);
  transition:transform .18s ease,background .18s ease;
}
.back-to-top:hover { background:#00a6cd; transform:translateY(-3px); }
.back-to-top:focus-visible { outline:3px solid #f6a003; outline-offset:3px; }
@media(max-width:850px){.back-to-top{right:16px;bottom:16px;width:42px;height:42px}}