<div class="wrapper">

  <div class="gold"><code>flex-grow: <strong>1</strong>;</code></div>
  <div class="red"><code>flex-grow: <strong>10</strong>;</code></div>
  <div class="blue"><code>flex-grow: <strong>3</strong>;</code></div>

</div>
* {
  box-sizing: border-box;
}

.wrapper {
  font-family: monospace;
  color: #fff;
  border: 2px solid #ddd;
  display: flex;
  height: 250px;
} 

.wrapper > div {
  padding: 56px 0;
  font-weight: 700;
  font-size: 1em;
  text-align: center;
}

.gold {
  background-color: gold;
  flex-grow: 1;
}

.red {
  background-color: red;
  flex-grow: 10;
}

.blue {
  background-color: steelblue;
  flex-grow: 3;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.