chromium/chrome/browser/resources/privacy_sandbox/privacy_sandbox_dialog_learn_more.html

<style include="cr-shared-style">
iron-collapse {
  --iron-collapse-transition-duration: 300ms;
}
.cr-secondary-text{
  margin-left: 4px;
}
</style>

<div>
  <cr-expand-button expanded="{{expanded}}">
    <div class="cr-secondary-text">
      {{title}}
    </div>
  </cr-expand-button>
  <cr-collapse id="collapse" opened="[[expanded]]">
    <slot></slot>
  </cr-collapse>
</div>