CSSとJavaScriptを使用して液体アニメーションをタップバー

<div class="container">
  <div class="bar">
    <div class="bar-item pre-active" onclick="changeActive(this)">
      <div class="bar-fluid"></div>
      <div class="drop"></div>
      <i class="far fa-calendar-alt"></i>
    </div>
    <div class="bar-item" onclick="changeActive(this)">
      <div class="bar-fluid"></div>
      <div class="drop"></div>
      <i class="far fa-sticky-note"></i>
    </div>
    <div class="bar-item" onclick="changeActive(this)">
      <div class="bar-fluid"></div>
      <div class="drop"></div>
      <i class="far fa-bell"></i>
    </div>
    <div class="bar-item" onclick="changeActive(this)">
      <div class="bar-fluid"></div>
      <div class="drop"></div>
      <i class="far fa-address-book"></i>
    </div>
  </div>
</div>

* {
  margin: 0px;
  padding: 0px;
  box-sizing: border-box;
}

.container {
  width: 100%;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: #fc5c65;
}

.bar {
  padding: 0px 10px;
  display: flex;
  align-items: center;
  background-color: #ffffff;
  border-radius: 10px 10px 20px 20px;
  box-shadow: 3px 3px 0px 0px rgb(235 59 90);
}

.bar .bar-item {
  position: relative;
  overflow: hidden;
  padding: 20px 25px;
  cursor: pointer;
}

.bar .bar-item i {
  z-index: 1;
  position: relative;
  color: #a4b0be;
  transition: all .3s ease-in-out;
}

.bar .bar-item.pre-active i {
  color: #fc5c65;
}

.bar .bar-item.active i {
  color: #fc5c65;
  animation: colour 1s ease-in-out;
}

.bar .bar-item.active .bar-fluid {
  position: absolute;
  top: 0px;
  left: 0px;
  background-color: #fc5c65;
  width: 100%;
  height: 0px;
  animation: fluid 1s ease-in-out;
}

.bar .bar-item.active .bar-fluid:before {
  content: '';
  position: absolute;
  top: 0px;
  left: -50%;
  background-color: #ffffff;
  width: 110%;
  height: 400%;
  border-radius: 50%;
}

.bar .bar-item.active .bar-fluid:after {
  content: '';
  position: absolute;
  top: 0px;
  right: -50%;
  background-color: #ffffff;
  width: 110%;
  height: 400%;
  border-radius: 50%;
}

.bar .bar-item.active .drop {
  position: absolute;
  top: -2.5px;
  left: 30.5px;
  background-color: #fc5c65;
  width: 2.5px;
  height: 2.5px;
  border-radius: 50%;
  animation: drop 1s ease-in-out;
}

@keyframes colour {
  0% { color: #a4b0be; }
  55% {
    color: #a4b0be;
    transform: scale(1);
  }
  60% {
    color: #fc5c65;
    transform: scale(1);
  }
  70% { transform: scale(1.1); }
  80% { transform: scale(1); }
}

@keyframes fluid {
  0% { height: 0px; }
  30% { height: 10px; }
  100% { height: 0px; }
}

@keyframes drop {
  20% { top: -2.5px; }
  50% { top: 21px; }
  51% { top: -2.5px; }
}

const preactiveItem = document.querySelector('.pre-active')
const barItems = document.querySelectorAll('.bar-item')

function changeActive (newActive) {
  preactiveItem.classList.remove('pre-active')
  barItems.forEach(element => {
    element.classList.remove('active')
  })
  newActive.classList.add('active')
}