Fieldset

Groups related controls under one legend.

Mailing address

Street

ZIP code

Show the markup

<fieldset class="cc-fieldset">
  <legend>Mailing address</legend>
  <div class="cc-field">
    <label class="cc-label" for="ex-fs-street">Street</label>
    <input class="cc-input" id="ex-fs-street" autocomplete="street-address">
  </div>
  <div class="cc-field" style="margin-bottom:0">
    <label class="cc-label" for="ex-fs-zip">ZIP code</label>
    <input class="cc-input cc-input--sm" id="ex-fs-zip" inputmode="numeric" autocomplete="postal-code">
  </div>
</fieldset>

Accessibility

Any group of radios or checkboxes belongs in a fieldset — the legend is announced with each control.
Keep legends short; they're repeated by assistive tech.