zen-8.x-7.0-alpha15/STARTERKIT/components/forms/form-item/form-item--radio.twig

<div class="form-item">
  <label class="form-item__label" for="group">Label for the group</label>
  <div class="form-item__description">
    Form group description.
  </div>
  <div class="form-item__group" id="group">
    <div class="form-item--radio {{modifier_class}}">
      <input class="form-item__widget" type="checkbox" id="option-1" value="1">
      <label class="form-item__label" for="option-1">Option 1</label>
      <div class="form-item__description">
        Form item description.
      </div>
    </div>
    <div class="form-item--radio {{modifier_class}}">
      <input class="form-item__widget" type="checkbox" id="option-2" value="2">
      <label class="form-item__label" for="option-2">Option 2</label>
      <div class="form-item__description">
        Form item description.
      </div>
    </div>
  </div>
</div>