govuk-frontend/dist/govuk/components/details/template-with-html.html

GOV.UK Frontend contains the code you need to start building a user interface for government platforms and services.

<details class="govuk-details">
  <summary class="govuk-details__summary">
    <span class="govuk-details__summary-text">
      Where to find your National Insurance Number
    </span>
  </summary>
  <div class="govuk-details__text">
    Your National Insurance number can be found on
<ul>
  <li>your National Insurance card</li>
  <li>your payslip</li>
  <li>P60</li>
  <li>benefits information</li>
  <li>tax return</li>
</ul>

  </div>
</details>