.back-to-top {
  box-sizing: border-box;
  position: fixed;
  bottom: $b2t-position-bottom;
  right: $b2t-position-right;
  z-index: $zindex-5;
  padding: 0 6px;
  width: hexo-config('back2top.scrollpercent') ? initial : 24px;
  background: $b2t-bg-color;
  font-size: $b2t-font-size;
  opacity: $b2t-opacity;
  color: $b2t-color;
  cursor: pointer;
  text-align: center;
  transition-property: bottom;
  the-transition();

  &.back-to-top-on {
    bottom: $b2t-position-bottom-on;
  }
  +tablet-mobile() {
    opacity: $b2t-opacity-hover;
    right: $b2t-position-right-mobile;
  }
}