

.cd-top {
  display: inline-block;
  height: 40px;
  width: 40px;
  position: fixed;
  bottom: 40px;
  right: 10px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.05); /*阴影效果*/
  /* image replacement properties */
  overflow: hidden;
  text-indent: 100%;
  white-space: nowrap;
  background: rgba(32, 98, 86, 0.6) url(../img/cd-top-arrow.svg) no-repeat center 50%;
  visibility: hidden;
  opacity:0.8; /*透明度 越大越不透明*/
  border-radius:5px; /*图片圆角*/
  -webkit-transition: opacity .3s 0s, visibility 0s .3s;
  -moz-transition: opacity .3s 0s, visibility 0s .3s;
  transition: opacity .3s 0s, visibility 0s .3s;
}
.cd-top.cd-is-visible, .cd-top.cd-fade-out, .no-touch .cd-top:hover {
  -webkit-transition: opacity .3s 0s, visibility 0s 0s;
  -moz-transition: opacity .3s 0s, visibility 0s 0s;
  transition: opacity .3s 0s, visibility 0s 0s;
}
.cd-top.cd-is-visible {
  /* the button becomes visible */
  visibility: visible;
  opacity: 1;
}
.cd-top.cd-fade-out {
  /* if the user keeps scrolling down, the button is out of focus and becomes less visible */
  opacity: .5;
}
.no-touch .cd-top:hover {
  background-color: #999999;
  opacity: 1;
}
@media only screen and (min-width: 768px) {
  .cd-top {
    right: 20px;
    bottom: 20px;
  }
}
@media only screen and (min-width: 1024px) {
  .cd-top {
    height: 50px;
    width: 50px;
    right: 30px;
    bottom: 30px;
  }
}
