/* ───── Back-to-top button ───── */
#back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  z-index: 999;
  background: rgba(0, 0, 0, 0.75);
  color: white;
  width: 50px;
  height: 50px;
  line-height: 50px;
  text-align: center;
  font-size: 28px;
  border-radius: 50%;
  text-decoration: none;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
  transition: all 0.3s ease;
  display: none; /* hidden until class .show is added */
}
#back-to-top.show {
  display: block;
}
#back-to-top:hover {
  background: rgba(0, 0, 0, 0.95);
  transform: scale(1.1);
}