<div class="container">
  <p class="column">150px</p>
  <p class="column">1fr</p>
  <p class="column">1fr</p>
  <p class="column">150px</p>    
</div>
.container {
  display: grid;
  grid-template-columns: 150px 1fr 1fr 150px;
  grid-template-rows: auto;
  grid-gap: .5em;
}

@media (max-width: 600px) {
  .container {
    grid-template-columns: 1fr 1fr;    
  }
}
/* etc: */

body {
  margin: 1.5em;
  font-size: 130%;
  font-family: monospace;
}

/* Etc: */

.column {
  background: #b3e888;
  padding: 1em;
  margin-top: 0;
  margin-bottom: 0;
  margin-left: 2px;  
}

.container {
  border: 5px solid black;
  padding: 1em;
  margin-bottom: 2em;
}

External CSS

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External JavaScript

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