<div class="grow">
  <div class="item">1<br>flex-grow-1</div>
  <div class="item">2<br>flex-grow-2</div>
  <div class="item">3<br>flex-grow-3</div>
</div>
.grow {
  display:flex;
  background-color: lightskyblue;
}

.item:nth-of-type(1) {
  flex-grow:1;
}
.item:nth-of-type(2) {
  flex-grow:2;
}
.item:nth-of-type(3) {
  flex-grow:3;
}

.item {
  background-color: red;
  color:#fff;
  margin: 10px;
  text-align: center;
  padding: 10px;
}

External CSS

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External JavaScript

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