input classes in bootstrap code example

Example: radio button bootstrap

<div class="btn-group btn-group-toggle" data-toggle="buttons">
  <label class="btn btn-secondary active">
    <input type="radio" name="options" id="option1" autocomplete="off" checked> Active
  </label>
  <label class="btn btn-secondary">
    <input type="radio" name="options" id="option2" autocomplete="off"> Radio
  </label>
  <label class="btn btn-secondary">
    <input type="radio" name="options" id="option3" autocomplete="off"> Radio
  </label>
</div>