/* create a flex container */

.flex-container {
  display: flex;
  background-color: DodgerBlue;
}

.flex-container > div {
  background-color: #f1f1f1;
  margin: 10px;
  padding: 20px;
  font-size: 30px;
}
/*
<div class="flex-container">
  <div>1</div>
  <div>2</div>
  <div>3</div>  
</div>
*/