govuk-frontend/dist/govuk/components/radios/template-small-with-conditional-reveal.html

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

<div class="govuk-form-group govuk-radios--small">
  <fieldset class="govuk-fieldset">
  <legend class="govuk-fieldset__legend">
    How do you want to be contacted?
  </legend>
  <div class="govuk-radios" data-module="govuk-radios">
    <div class="govuk-radios__item">
      <input class="govuk-radios__input" id="how-contacted-2" name="how-contacted-2" type="radio" value="email" data-aria-controls="conditional-how-contacted-2">
      <label class="govuk-label govuk-radios__label" for="how-contacted-2">
        Email
      </label>
    </div>
    <div class="govuk-radios__conditional govuk-radios__conditional--hidden" id="conditional-how-contacted-2">
      <label class="govuk-label" for="context-email">Foo</label>
<input class="govuk-input govuk-!-width-one-third" name="context-email" type="text" id="context-email">
    </div>
    <div class="govuk-radios__item">
      <input class="govuk-radios__input" id="how-contacted-2-2" name="how-contacted-2" type="radio" value="phone">
      <label class="govuk-label govuk-radios__label" for="how-contacted-2-2">
        Phone
      </label>
    </div>
    <div class="govuk-radios__item">
      <input class="govuk-radios__input" id="how-contacted-2-3" name="how-contacted-2" type="radio" value="text">
      <label class="govuk-label govuk-radios__label" for="how-contacted-2-3">
        Text message
      </label>
    </div>
  </div>
</fieldset>
</div>