Demo: CSS inset-block

<div class='container'>
  <div class='box'>I am a box with inset-block!</div>
</div>

.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: #f0f0f0;
  position: relative;
}

.box {
  width: 200px;
  height: 100px;
  background-color: #4CAF50;
  color: white;
  display: flex;
  justify-content: center;
  align-items: center;
  inset-block: 20px 0; /* 20px top, 0px bottom */
  position: absolute;
}

// No JavaScript required for this demo