Button Group

Default 

<div class="ButtonGroup js-ButtonGroupDemo">
  <button class="Button">
    Button 1
  </button>
  <button class="Button is-active">
    Button 2
  </button>
  <button class="Button">
    Button 3
  </button>
</div>

Primary 

<div class="ButtonGroup js-ButtonGroupDemo">
  <button class="Button Button--primary">
    Button 1
  </button>
  <button class="Button Button--primary is-active">
    Button 2
  </button>
  <button class="Button Button--primary">
    Button 3
  </button>
</div>

Status 

<div class="ButtonGroup js-ButtonGroupDemo" style="width: 250px">
  <button class="Button Button--yesDefault u-size1of3">
    Going
  </button>
  <button class="Button Button--maybeDefault u-size1of3">
    Maybe
  </button>
  <button class="Button Button--noDefault u-size1of3">
    No
  </button>
</div>