#btnScrollTop {
  position: fixed;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%) scale(0.5); /* Escalado inicial */
  z-index: 1000;

  width: 3.5rem;
  height: 3.5rem;
  background: #fff;
  border-radius: 50%;
  border: none;

  font-size: 2.5rem;
  color: #113b8a;
  cursor: pointer;

  opacity: 0;
  pointer-events: none;

  transition:
    opacity 0.3s ease,
    transform 0.3s ease;
}

/* Estado visible: se activa vía JS */
#btnScrollTop.visible {
  pointer-events: auto;
}