.sts-top {
  display: inline-block;
  height: 40px;
  width: 40px;
  position: fixed;
  bottom: 45px;
  right: 10px;
  overflow: hidden;
  background: url(../sts-scrolltotop/sts-scrolltotop.png)no-repeat 50% 50%;
  visibility: hidden;
  background-color: #2E8B57;
  border-radius: 50%;
  opacity: 0;
  filter: drop-shadow(3px 3px 3px #4F4F4F)
}
.sts-top.sts-visible {
  visibility: visible;
  opacity: 1;
}
.sts-top.sts-visible:hover {
  background-color: #B40404;
  border-radius: 50%;
}