<div class="box">
  <div class="item">75px</div>
  <div class="item">75px</div>
  <div class="item">75px</div>
  <div class="item">1fr</div>
  <div class="item">1fr</div>
  <div class="item">1fr</div>
  <div class="item">45vh</div>
  <div class="item">45vh</div>
  <div class="item">45vh</div>
</div>
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.box {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 75px 1fr 45vh;
  grid-gap: 16px;
  height: 100vh;
}

.item {
  background-color: tomato;
  color: white;
  font-size: 1.75em;
  text-align: center;
  font-family: monospace;
  padding: 16px 0;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.