<div class="container">
    <div class="item item-1">1</div>
    <div class="item item-2">2</div>
    <div class="item item-3">3</div>
</div>
html {
  background: #f6faff;
}

/*-- --*/
.container {
  background-color: darkslategrey;
  padding: 1rem;
  display: flex;
  flex-direction: row;
}
.item {
  font-size: 2rem;
  line-height: 1;
  text-align: center;
  width: 3rem;
  padding: 2rem 1rem;
  background: #e2f0ef;
  border: 3px solid #51aaa3;
  color: #51aaa3;
  margin: 0.375rem; 
  flex-grow: 1;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js