Add checkbox disabled state styles

[Wolfr]

Would probably be a good idea to add another radio button so you can test the toggling between the two

<div class="flex-group">
    <div class="input-radio-wrapper">
      <input type="radio" name="test" class="input-radio" id="test-radio1" disabled="">
      <label for="test-radio1" class="input-radio-label">
        <div class="input-radio-button"></div>
      </label>
    </div>

    <div class="input-radio-wrapper">
      <input type="radio" name="test" class="input-radio" id="test-radio2" checked>
      <label for="test-radio2" class="input-radio-label">
        <div class="input-radio-button"></div>
      </label>
    </div>

    <div class="input-radio-wrapper">
      <input type="radio" name="test" class="input-radio" id="test-radio3">
      <label for="test-radio3" class="input-radio-label">
        <div class="input-radio-button"></div>
      </label>
    </div>
</div>