url(r'^login$' ,  LoginView.as_view(template_name='login.html'), name='Login' , kwargs={"authentication_form": LoginUser}),

class LoginUser(AuthenticationForm):
    username = forms.CharField(widget=TextInput(attrs={'style':'font-size : 20px;color:white','placeholder': 'Username'}))
    password = forms.CharField(widget=PasswordInput(attrs={'placeholder':'Password' , 'style' : 'font-size : 20px;color:white'}))

class LoginUser(AuthenticationForm):
    username = forms.CharField(widget=TextInput(attrs={'class':'your_class', 'placeholder': 'Username'}))
    password = forms.CharField(widget=PasswordInput(attrs={'class':'your_class', 'placeholder': 'Password'}))