Demo: CSS margin-inline

<div class='container'>
  <div class='box'>Box 1</div>
  <div class='box'>Box 2</div>
</div>

.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.box {
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  margin-inline: 15px;
  border-radius: 5px;
  text-align: center;
}

// No JavaScript required for this demo