Django Crispy表单中的自定义CSS

forms.py：

from django import forms

from .models import SignUp


from crispy_forms.helper import FormHelper
from crispy_forms.layout import Submit, Layout, Field

class ContactForm(forms.Form):
    full_name = forms.CharField( required=False)
    email = forms.EmailField()
    message = forms.CharField()




class SignUpForm(forms.ModelForm):


        class Meta:
            model = SignUp
            fields = ['full_name', 'email']
            ### exclude = ['full_name']
            helper = FormHelper()
            helper.layout = Layout(
            Field('full_name', css_class='container'),
            Field('email', css_class='input-sm'),
                ) 

我得到的HTML显示它使用不同的CSS类，而不是布局中的类。我错过什么了吗？我做错什么了吗？如何将自定义CSS添加到表单中

HTML:

全名
电子邮件*

<div id="div_id_full_name" class="form-group"> <label for="id_full_name" class="control-label ">
                Full name
            </label> <div class="controls "> <input class="textinput textInput form-control" id="id_full_name" maxlength="120" name="full_name" type="text" /> </div> </div> <div id="div_id_email" class="form-group"> <label for="id_email" class="control-label  requiredField">
                Email<span class="asteriskField">*</span> </label> <div class="controls "> <input class="emailinput form-control" id="id_email" maxlength="254" name="email" type="email" required /> </div> </div>