Demo: CSS margin-inline-end

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

.container {
  display: flex;
  justify-content: space-between;
  padding: 20px;
  background-color: #f0f0f0;
}

.box {
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  margin-inline-end: 20px;
}

.box:last-child {
  margin-inline-end: 0;
}

// No JavaScript required for this demo