#scrollTopBtn {
  display: none;
  position: fixed;
  bottom: 30px;
  right: 30px;
  z-index: 99;
  width: 48px;
  height: 48px;
  border: none;
  border-radius: 50%;
  background-color: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(5px);
  cursor: pointer;
  opacity: 0;
  /* start transparant */
  transition: opacity 0.3s ease, transform 0.3s ease, background-color 0.3s ease;
}

#scrollTopBtn.show {
  display: block;
  opacity: 1;
}

#scrollTopBtn:hover {
  background-color: rgba(255, 255, 255, 0.25);
  transform: scale(1.1);
}

.arrow-up {
  position: relative;
  display: inline-block;
  width: 0;
  height: 0;
  border-left: 8px solid transparent;
  border-right: 8px solid transparent;
  border-bottom: 10px solid white;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}