AfterAales/themes/next/source/css/_common/components/back-to-top-sidebar.styl

.back-to-top {
  background: transparent;
  margin: 20px - $sidebar-offset -10px -20px;
  opacity: 0;

  if (!hexo-config('back2top.scrollpercent')) {
    span {
      display: none;
    }
  }

  &.back-to-top-on {
    cursor: pointer;
    opacity: $b2t-opacity;

    &:hover {
      opacity: $b2t-opacity-hover;
    }
  }
}