<p>Check <a href="https://codepen.io/matuzo/post/animating-css-grid-layout-properties">this post</a> for more details</p>

<button class="js-button">Animate</button>

<div class="grid js-grid">
  <article class="item">
    <h2>Element 1</h2>
  </article>
  <article class="item">
    <h2>Element 2</h2>
  </article>
  <article class="item">
    <h2>Element 3</h2>
  </article>
  <article class="item">
    <h2>Element 4</h2>
  </article>
  <article class="item">
    <h2>Element 5</h2>
  </article>
  <article class="item">
    <h2>Element 6</h2>
  </article>  
  <article class="item">
    <h2>Element 7</h2>
  </article>
  <article class="item">
    <h2>Element 8</h2>
  </article>
  <article class="item">
    <h2>Element 9</h2>
  </article>  
  <article class="item">
    <h2>Element 10</h2>
  </article>
  <article class="item">
    <h2>Element 11</h2>
  </article>
  <article class="item">
    <h2>Element 12</h2>
  </article>
</div>

.grid {
  display: grid;
  grid-template-columns: 200px 200px 200px;
  grid-template-rows: 100px;
  grid-gap: 20px;
  transition: all 1s;
}

.grid--full {
  grid-template-columns: 300px 300px 300px;
  grid-template-rows: 200px;
  grid-gap: 10px;
}

button {
  background-color: #123456;
  color: #ffffff;
  margin: 2rem 0;
  padding: 1.4rem;
  border: none;
  border-radius: 5px;
  text-transform: uppercase;
  font-size: 1.2rem;
}

dt {
  font-weight: bold;
  margin-bottom: 0.5rem;
}

document.querySelector('.js-button').addEventListener('click', function() {
  console.log('test')
  document.querySelector('.js-grid').classList.toggle('grid--full')
})