#back-to-top_button {
  border-radius: 4px;
  bottom: 100px;
  display: inline-block;
  height: 50px;
  opacity: 0;
  position: fixed;
  right: 22px;
  text-align: center;
  transition: background-color 0.3s, opacity 0.5s, visibility 0.5s;
  visibility: hidden;
  width: 50px;
  z-index: 1000;
}
#back-to-top_button.show {
  opacity: 1;
  visibility: visible;
}
#back-to-top_button svg {
  fill: #fff;
  display: inline-block;
  height: 22px;
  left: 50%;
  margin: 0;
  position: absolute;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 22px;
}