{{ govuk.details(
    summary = "Summary text",
    contentHtml = "<p>We need to know your nationality so we can work out which elections you’re entitled to vote in.</p> <a href=\"#\">I can’t provide my nationality</a>"
) }}
<%= govuk.details(
    summary: "Summary text",
    contentHtml: "<p>We need to know your nationality so we can work out which elections you’re entitled to vote in.</p> <a href=\"#\">I can’t provide my nationality</a>"
) %> 
<details class="gv-c-details">
    <summary class="gv-c-details__summary">
        <span class="gv-c-details__summary-text">Summary text</span>
    </summary>
    <div class="panel panel-border-narrow">

        <p>We need to know your nationality so we can work out which elections you’re entitled to vote in.</p> <a href="#">I can’t provide my nationality</a>

    </div>
</details>
{
  "summary": "Summary text",
  "contentHtml": "<p>We need to know your nationality so we can work out which elections you’re entitled to vote in.</p> <a href=\"#\">I can’t provide my nationality</a>"
}