Vertical Bars Transition

HTML

<div class="container">
    <div class="bar"></div>
    <div class="bar"></div>
    <div class="bar"></div>
    <div class="bar"></div>
    <div class="bar"></div>
  </div>

index2.html script

<script>
    var nums = [2.9, 4.1, 2.1, 4.4, 2.8]

    function changeHeight() {
      const bars = document.querySelectorAll('.bar2');
      var scroll = (window.pageYOffset / 5);

      bars.forEach((col, key) => {
        var height = Math.min(100 - (scroll * nums[key]));
        col.style.height = height + '%';
      })
    }

    window.addEventListener('scroll', function() {
      requestAnimationFrame(changeHeight);
    })
  </script>

index3.html script

<script>
    function changeHeight() {
      const bars = document.querySelectorAll('.bar3');
      var height = Math.max(100 - window.pageYOffset);

      bars.forEach((col, key) => {
        if(height > 0) {
          col.style.height = height + '%';
        } else {
          col.style.height = 0;
        }
      })
    }

    window.addEventListener('scroll', function() {
      requestAnimationFrame(changeHeight);
    })
  </script>

CSS

body {
  margin: 0;
}

.container {
  background-image: url('image.jpg');
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  height: 140vh;
  display: grid;
  grid-template-columns: repeat(5, 1fr);
}

.bar {
  background: #FBD84A;
  height: 100vh;
  transition: height 2.3s;
  animation: animate forwards;
}

.bar:nth-child(1) {
  animation-duration: 3s;
}
.bar:nth-child(2) {
  animation-duration: 4s;
}
.bar:nth-child(3) {
  animation-duration: 3.5s;
}
.bar:nth-child(4) {
  animation-duration: 2.9s;
}
.bar:nth-child(5) {
  animation-duration: 3.1s;
}

@keyframes  animate {
  from {
    height: 100vh;
  }
  to {
    height: 0;
  }
}

/* Index 2 */
.bar2 {
  background: #FBD84A;
  height: 100vh;
  transition: height 2.3s;
}

/* Index 3 */
.bar3 {
  background: #FBD84A;
  height: 100vh;
  transition: height 2s;
  position: fixed;
  width: 20%;
  height: 100vh;
}
.bar3:nth-child(1) {
  top: 0;
}
.bar3:nth-child(2) {
  top: 0;
  left: 20%;
  transition-delay: 0.2s;
}
.bar3:nth-child(3) {
  bottom: 0;
  left: 40%;
}
.bar3:nth-child(4) {
  bottom: 0;
  left: 60%;
  transition-delay: 0.2s;
}
.bar3:nth-child(5) {
  top: 0;
  left: 80%;
}

Image Source