<div class="container">
  <div class="side-1">Side 1</div>  
  <div class="content">Content<br>…<br>…<br>…</div>
  <div class="side-2">Side 2</div>  
</div>

.container > * {
  margin-bottom: .5em;
}

.container > :last-child {
  margin: 0;
}

@media screen and (min-width: 37.5em) {
  .container {
    display: grid;
    grid-template-columns: 1fr 3fr 1fr;
    gap: 0.5rem;
  }
  
  .container > * {
    margin-bottom: 0;
  }
}

/* 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: 1em;
}

.container > * {
  padding: 0.5em;
  text-align: center;
  background: #e5e3de;
  font-weight: bold;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.