govuk-frontend/dist/govuk/components/error-summary/template-default.html

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

<div class="govuk-error-summary" data-module="govuk-error-summary">
  <div role="alert">
    <h2 class="govuk-error-summary__title">
      There is a problem
    </h2>
    <div class="govuk-error-summary__body">
        <ul class="govuk-list govuk-error-summary__list">
          <li>
            <a href="#example-error-1">The date your passport was issued must be in the past</a>
          </li>
          <li>
            <a href="#example-error-2">Enter a postcode, like AA1 1AA</a>
          </li>
        </ul>
    </div>
  </div>
</div>