Edit in JSFiddle

$div = document.querySelector('.wrapper');
$div.addEventListener('click', (event) => {
  [...$div.children].forEach(element => {
    element.classList.toggle('active');
  })
});

<div class="wrapper">
  <div class="box left"></div>
  <div class="box right"></div>
</div>

body {
  background-color: #333;
}

.wrapper {
  display: flex;
  justify-content: space-between;
  align-items: center;
  width: 32px;
  height: 32px;
  margin: 32px;
}

.box {
  width: 0;
  height: 24px;
  transition: 0.2s all;
  border-left: 8px solid white;
  border-top: 0 solid transparent;
  border-bottom: 0 solid transparent;
}

.box.active {
  border-top: 6px solid transparent;
  border-bottom: 6px solid transparent;
  border-left: 10px solid white;
}

.left {
  margin-left: 6px;
}

.right {
  margin-right: 6px;
}

.right.active {
  height: 0;
}

.left.active {
  height: 12px;
}