Add CSS to Form Type is Symfony2

I have an edit form, The form is made through symfony2 Form types. I checked the documentation but couldn't find any option for adding CSS to the form. The form display the data correctly and everything is fine what I want to do is to add styling to each field.

My Edit Type is

 public function buildForm(FormBuilder $builder, array $options)
{
    $builder
    ->add('id', 'hidden')
    ->add('patent_name', 'text', array('label' => 'Patent Name'))
    ->add('description', 'textarea', array('label' => 'Description', 'required' => false))
    ->add('appln_auth','text', array('label' => 'Application Authorization'))
    ;
}

Anyone has any idea ho I can add css ?

Thanks