flex-grow

flex-grow: 1;

flex-grow: 2;

flex-grow: 3;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">I grow</div>
  <div>Item Two</div>
  <div>Item Three</div>
</section>

.default-example {
  border: 1px solid #c5c5c5;
  width: auto;
  max-height: 300px;
  display: flex;
}

.default-example > div {
  background-color: rgb(0 0 255 / 0.2);
  border: 3px solid blue;
  margin: 10px;
  flex-grow: 1;
  flex-shrink: 1;
  flex-basis: 0;
}

/* <number> values */
flex-grow: 3;
flex-grow: 0.6;

/* Global values */
flex-grow: inherit;
flex-grow: initial;
flex-grow: revert;
flex-grow: revert-layer;
flex-grow: unset;

<h1>This is a <code>flex-grow</code> example</h1>
<p>
  A, B, C, and F have <code>flex-grow: 1</code> set. D and E have
  <code>flex-grow: 2</code> set.
</p>
<div id="content">
  <div class="box1">A</div>
  <div class="box2">B</div>
  <div class="box3">C</div>
  <div class="box4">D</div>
  <div class="box5">E</div>
  <div class="box6">F</div>
</div>

#content {
  display: flex;
}

div > div {
  border: 3px solid rgb(0 0 0 / 20%);
}

.box1,
.box2,
.box3,
.box6 {
  flex-grow: 1;
}

.box4,
.box5 {
  flex-grow: 2;
  border: 3px solid rgb(0 0 0 / 20%);
}

.box1 {
  background-color: red;
}
.box2 {
  background-color: lightblue;
}
.box3 {
  background-color: yellow;
}
.box4 {
  background-color: brown;
}
.box5 {
  background-color: lightgreen;
}
.box6 {
  background-color: brown;
}