Use the order Property to Rearrange Items

Summary

The order property is used to tell CSS the order of how flex items appear in the flex container.

Final Code

<style>
  #box-container {
    display: flex;
    height: 500px;
  }
  #box-1 {
    background-color: dodgerblue;
    order: 2;
    height: 200px;
    width: 200px;
  }

  #box-2 {
    background-color: orangered;
    order: 1;
    height: 200px;
    width: 200px;
  }
</style>

<div id="box-container">
  <div id="box-1"></div>
  <div id="box-2"></div>
</div>