List unstyled

When i create a list-group in the app structure i can’t apply list-unstyled (does not work).
So i added the code (from bootstrap documentation) below in the code area :

<ul class="list-unstyled">
  <li>This is a list.</li>
  <li>It appears completely unstyled.</li>
  <li>Structurally, it's still a list.</li>
  <li>However, this style only applies to immediate child elements.</li>
  <li>Nested lists:
    <ul>
      <li>are unaffected by this style</li>
      <li>will still show a bullet</li>
      <li>and have appropriate left margin</li>
    </ul>
  </li>
  <li>This may still come in handy in some situations.</li>
</ul>

But in this case it works, but i don’t see the list-group anymore in the app structure. If i add in the code the class list-group manually, it does not appears neither.

What is the best practice and how to deal with this? I guess it applies to other cases.