.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  width: 50px;
  height: 50px;
  background: #3498db;
  color: white;
  border-radius: 50%;
  display: flex;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  opacity: 0;
  transition: all 0.3s;
  box-shadow: 0 2px 5px rgba(0,0,0,0.2);
  font-size: 30px;
  font-weight: bold;
  z-index: 999;
  text-decoration: none;
}
.back-to-top.visible {
  opacity: 1;
}
.back-to-top:hover {
  background: #2980b9;
  transform: translateY(-3px);
}