<div class="site-container">
  <div class="card card--collapsible">
    <h2 class="card__title">Click to toggle</h2>
    <p>This example is using View Transitions API to demonstrate how easily the widths, position, and shadow attributes are transitioned dynamically and seamlessly.</p>
  </div>
</div>

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  font: 1em/1.6 sans-serif;
  background: #ddd;
  margin: 0;
}

p {
  margin-bottom: 0;
}

p + p {
  margin-top: 1.5em;
}

.site-container {
  padding: 2rem;
  display: grid;
  place-items: center;
  min-height: 100vh;
}

.card {
  max-width: 480px;
  background: white;
  padding: 1.5rem;
  border-radius: 0.5rem;
  cursor: pointer;
  box-shadow: 0 0.25rem 0.5rem hsl(0 0 0 / 15%);

  & + & {
    margin-top: 1.5em;
  }
}

.card--collapsible {
  position: relative;
  overflow: hidden;
  height: 120px;
  view-transition-name: card;
  &::before {
    content: "+";
    position: absolute;
    right: 1em;
    top: 1em;
    line-height: 1;
    font-weight: bold;
    width: 1em;
    text-align: center;
  }
  &::after {
    content: "";
    position: absolute;
    display: block;
    width: 100%;
    bottom: 0;
    height: 2rem;
    background: linear-gradient(to bottom, transparent, white);
  }
}

.card__title {
  font-size: 1.25em;
  margin-top: 0;
}

.card--expanded {
  height: auto;
  box-shadow: 0 1rem 2rem hsl(0 0 0 / 35%);
  &::after {
    background: none;
  }
  &::before {
    content: "–";
  }
}

::view-transition-group(card) {
  animation-duration: 0.75s;
}

const card = document.querySelector(".card--collapsible");

card?.addEventListener("click", () => {
  if (!document.startViewTransition) {
    card.classList.toggle("card--expanded");
    return;
  }

  document.startViewTransition(() => {
    card.classList.toggle("card--expanded");
  });
});