<div class="container">
  <div class="item item--1">
    Item 1
  </div>
  <div class="item item--2">
    Item 2
  </div>
  <div class="item item--3">
    Item 3
  </div>  
</div>
.item--3 {
  justify-self: end; /* ignored */
}

/* ETC (Formatting only): */

body {
  margin: 1.5em;
  font-size: 130%;
  font-family: sans-serif;
  background: #F2F0EC;
  color: #2E2C08;
}

.container { 
  border: 10px solid #2E2C08;
  background: white;  
  padding: 1rem;
}

.item {
  margin: 0.25rem;
  padding: 0.5em;
  text-align: center;
  background: #e5e3de;
  font-weight: bold;
}

fieldset {
  border: #abab9d 1px solid;
  padding: 0;
  margin-bottom: 2em; 
}

label {
  display: inline-block;
  padding: 0.5em;
  cursor: pointer;
}

.active {
  background: #abab9d;
}

/* This pen styling */

.container {
  display: flex;
  height: 10em;  
}

.item {  
  padding: 1em;
  text-align: center;
  height: 5em;
  min-width: 5em;  
}

.item--3 {
  background: #abab9d;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.