<div class="post">
  <h2>Post</h2>
</div>

<div class="post -large">
  <h2>Post Large</h2>
</div>

.post {
  container-type: inline-size;
}
.post.-large {
  container-name: post-large;
}

h2 {
  margin-block: 0.4em;
}

@container (min-width: 480px) {
  .post h2 {
    font-size: 3em;
  }
}
@container post-large (min-width: 480px) {
  .post h2 {
    color: #faa;
  }
}