Below is an example of how to set up a commenting form in Bootstrap 4.
{# @var commentsWork \twentyfourhoursmedia\commentswork\services\CommentsWorkService #}
{% set commentsWork = craft.commentsWork.service %}
{% if not currentUser and not commentsWork.allowAnonymous(entry) %}
<p>Anonymous commenting is not allowed. Please login.</p>
{% else %}
<div class="card bg-light">
<div class="card-header">
Leave a comment
</div>
<div class="card-body">
<form method="post" action="{{ url('/actions/comments-work/default/post-comment') }}">
{{ csrfInput() }}
{{ signCommentForm(entry) }}
<input name="redirect" value="{{ craft.app.request.url }}#comments" type="hidden"/>
<input name="elementId" value="{{ entry.id }}" type="hidden"/>
<input name="siteId" value="{{ entry.siteId }}" type="hidden"/>
<input name="commentFormat" value="text" type="hidden"/>
<div class="form-group">
<label for="comment-title">Title</label>
<input name="title" id="comment-title" type="text" class="form-control"/>
</div>
<div class="form-group">
<label for="comment-content">Comment</label>
<textarea name="comment" rows="5" id="comment-content" class="form-control"></textarea>
</div>
<div>
<input type="submit" class="btn btn-primary" value="Post comment"/>
</div>
</form>
</div>
</div>
{% endif %}