.back-to-top {
  position: fixed;
  right: clamp(18px, 3vw, 32px);
  bottom: clamp(18px, 3vw, 32px);
  z-index: 900;
  display: grid;
  width: 50px;
  height: 50px;
  place-items: center;
  border: 1px solid rgba(107, 231, 241, .45);
  border-radius: 50%;
  background: linear-gradient(145deg, #0b5870, #063348);
  color: #fff;
  box-shadow: 0 13px 28px rgba(2, 20, 34, .34), 0 0 0 5px rgba(23, 193, 216, .08);
  font: 800 22px/1 'Manrope', sans-serif;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(14px) scale(.92);
  transition: opacity .22s ease, visibility .22s ease, transform .22s ease, background .22s ease, box-shadow .22s ease;
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0) scale(1);
}

.back-to-top:hover,
.back-to-top:focus-visible {
  background: linear-gradient(145deg, #14bfd6, #08788f);
  box-shadow: 0 17px 34px rgba(2, 20, 34, .4), 0 0 0 6px rgba(23, 193, 216, .14);
  transform: translateY(-3px) scale(1.03);
  outline: none;
}

@media (max-width: 560px) {
  .back-to-top {
    right: 16px;
    bottom: 16px;
    width: 46px;
    height: 46px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .back-to-top { transition: none; }
}