.page-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 1000;
  border: none;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity 0.3s ease,
              transform 0.4s ease;
  padding: 0;
  background: none;
}
button#pageTop a {
    display: block;
    padding: 16px 32px;
    background: #7f9a78;
    border-radius: 25px;
    font-size: 16px;
    font-weight: 700;
    color: #fff;
}
.page-top.is-show {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

/* 一番下付近で少し上に上がる */
.page-top.is-bottom {
  bottom: 50px;
}
.page-top.is-show.is-bottom {
  transform: translateY(-64px);
}