<div class="container">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
</div>

.container {
  display: flex;
}

.item {
  margin: 10px;
  padding: 20px;
  background-color: #f0f0f0;
  text-align: center;
}

.item:nth-child(1) {
  order: 3;  /* Moves this item to the end */
}

.item:nth-child(2) {
  order: 1;  /* Moves this item to the beginning */
}

.item:nth-child(3) {
  order: 2;  /* This item is in the middle */
}