.back-to-top {
  position: fixed;
  right: 20px;
  bottom: 20px;
  display: grid;
  place-content: center;
  height: 40px;
  width: 40px;
  padding: 0;
  font-size: 17px;
  appearance: none;
  background-color: white;
  border: none;
  cursor: pointer;
  transition-duration: 0.2s;
  z-index: z-index(burger);
}
.back-to-top:active {
  transform: scale(0.9);
  transition-duration: 0.2s;
}

.btt-is--visible {
  visibility: visible;
  opacity: 1;
}

.btt-is--fade-out {
  opacity: 0.5;
}