/*  Back Top Button  */
#back-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
}
#back-top a {
  background: rgba(0, 0, 0, 0.45);
  -webkit-border-radius: 7px;
  -moz-border-radius: 7px;
  -webkit-transition: 1s;
  -moz-transition: 1s;
  transition: 1s;
  width: 40px;
  height: 40px;
  display: block;
  font-size: 36px;
  color: #fff;
  text-align: center;
  border-radius: 3px 3px;
  text-decoration: none;
}
#back-top a:hover {
  background-color: #3C5494;
}

#back-top i {
    font-size: 24px;
    line-height: 40px;
    vertical-align: top;
}
/* 向上图标透明白色 */
.fa-chevron-up:before {
    color: rgba(252,252,252,0.81);
}
/*  Back Top Button  End */