#updown {
  width: 40px;
  line-height: 1;
  font-size: 4vw;
  color: white;
  position: fixed;
  bottom: 1vw;
  left: 1vw;
  text-shadow: 1px 1px 0px #000;
  cursor: pointer;
}
#updown.up::before {
  content: '\2191';
}
#updown.down::before {
  content: '\2193';
}