.back-to-top {
  position: fixed;
  bottom: 120px;
  right: 20px;
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background-color: #333;
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.3s ease-in-out;
  z-index: 10000;
}

@media (max-width: 768px) {
  .back-to-top {
    bottom: 80px;
    right: 15px;
    width: 40px;
    height: 40px;
  }
}

.back-to-top.visible {
  opacity: 1;
}

.back-to-top:hover {
  background-color: #555;
}