Customizing Symfony 2 form with bootstrap

I believe what you are looking for is found in the Symfony docs at Rendering each field manually. So you want to do something like this for your form then:

<div class="panel-body">   {{ form_start(edit_form  }}   <div class="form-group">        {{ form_label(edit_form.categoryName, 'CategoryName', {'label_attr': {'class': 'control-label col-xs-2'}}) }}        <div class="col-xs-6">            {{ form_widget(edit_form.categoryName, {'attr': {'class': 'form-control'}})  }}        </div>     </div>     <div class="form-group">        <div class="col-xs-offset-2 col-xs-10">            <button type="submit" class="btn btn-primary">Edit</button>        </div>     </div>  {{ form_end(form) }}</div>

Or something along these lines. As you can see, you can add classes to the twig rendered forms. for a complete reference of the twig templating functions, see the docs Twig Reference

If you are rendering the button with twig as well, then you could do this:

<div class="form-group">    <div class="col-xs-offset-2 col-xs-10">        {{ form_widget(form.editButton, {'attr': {'class': 'btn btn-primary'}}) }}    </div> </div>