.back_to_top_span {margin-bottom:30px}

.back_to_top {
  --offset: 1500px; 
  position: sticky;
  bottom:7vw;  
  left:100%; 
  margin-top: calc(100vh + var(--offset));
  padding:0;
  display: table-cell;
  width: 16vw;
  height: 0;
  padding-bottom: 16vw;
  background:var(--blue);
  border-radius:10px;
  opacity:0.4;
  transition: all 0.4s ease;
  z-index:50;
}

.back_to_top:before {
  content:"";
  position:absolute;
  inset:30%;
  transform:translateY(20%) scale(0.8) rotate(-45deg);
  border-top:5px solid #fff;
  border-right:5px solid #fff;
  transition: all 0.4s ease;
}

.back_to_top:hover {opacity:0.6;transition: all 0.4s ease}
.back_to_top:hover::before	{transform:translateY(20%) scale(1) rotate(-45deg);transition: all 0.4s ease}


@media only screen and (min-width: 350px) {
  .back_to_top {width: 14vw;padding-bottom: 14vw}
}
@media only screen and (min-width: 450px) {
  .back_to_top {width: 12vw;padding-bottom: 12vw}
}
@media only screen and (min-width: 600px) {
  .back_to_top {width: 9vw;padding-bottom: 9vw}
}
@media only screen and (min-width: 700px) {
  .back_to_top {width: 8vw;padding-bottom: 8vw}
}
@media only screen and (min-width: 900px) {
  .back_to_top {width: 7vw;padding-bottom: 7vw}
}
@media only screen and (min-width: 1050px) {
  .back_to_top {width: 6vw;padding-bottom: 6vw}
}