How to change the position of an element in flex container?

I want to take element 3 to the right of screen. This is an example from W3School

.flex-container {
      display: flex;
      background-color: DodgerBlue;
    }
    
    .flex-container > div {
      background-color: #f1f1f1;
      margin: 10px;
      padding: 20px;
      font-size: 30px;
    }

<h1>Create a Flex Container</h1>

<div class="flex-container">
  <div>1</div>
  <div>2</div>
  <div>3</div>  
</div>

How can I do this when I’m using flex display?

>Solution :

This is somewhat a hack, but it does work JSFiddle

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

.flex-container > div {
  background-color: #f1f1f1;
  margin: 10px;
  padding: 20px;
  font-size: 30px;
}

.flex-container > div:nth-child(3) {
  margin-left:auto;
}

Example