Зеленая кнопка "Вверх" с плавным эффектом появления

<style>.material-scrolltop {
  display: block;
  position: fixed;
  width: 0;
  height: 0;
  bottom: 23px;
  right: 23px;
  padding: 0;
  overflow: hidden;
  outline: none;
  border: none;
  border-radius: 2px;
  box-shadow: 0 3px 10px rgba(0, 0, 0, 0.5);
  cursor: hand;
  border-radius: 50%;
  background: #4caf50;
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
  -webkit-transition: all 0.3s cubic-bezier(0.25, 0.25, 0, 1);
  -ms-transition: all 0.3s cubic-bezier(0.25, 0.25, 0, 1);
  -moz-transition: all 0.3s cubic-bezier(0.25, 0.25, 0, 1);
  -o-transition: all 0.3s cubic-bezier(0.25, 0.25, 0, 1);
  transition: all 0.3s cubic-bezier(0.25, 0.25, 0, 1);
}

.material-scrolltop:hover {
  background-color: #4caf50;
  text-decoration: none;
  box-shadow: 0 3px 10px rgba(0, 0, 0, 0.5), 0 3px 15px rgba(0, 0, 0, 0.5);
}

.material-scrolltop::before {
  position: absolute;
  top: 50%;
  left: 50%;
  -webkit-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  -moz-transform: translate(-50%, -50%);
  -o-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
  content: "";
  width: 0;
  border-radius: 100%;
  background: #66bb6a;
}

.material-scrolltop:active::before {
  width: 120%;
  padding-top: 120%;
  -webkit-transition: all 0.2s ease-out;
  -ms-transition: all 0.2s ease-out;
  -moz-transition: all 0.2s ease-out;
  -o-transition: all 0.2s ease-out;
  transition: all 0.2s ease-out;
}

.material-scrolltop.reveal {
  width: 56px;
  height: 56px;
}

.material-scrolltop span {
  display: block;
  font-size: 25px;
  color: #fff;
}

.material-scrolltop,
.material-scrolltop::before {
  background-image: url(/top-arrow.svg);
  background-position: center 50%;
  background-repeat: no-repeat;
}</style>

<script src="/material-scrolltop.js"></script>
  <button class="material-scrolltop" type="button"></button>
  <script>
  $(document).ready(function() {
  $('body').materialScrollTop({
  revealElement: 'header',
  revealPosition: 'bottom',
  onScrollEnd: function() {
  console.log('Scrolling End');
  }
  });
  });
  </script>