如何在Symfony表单中设置下拉列表的子元素的样式

{% block choice_widget_collapsed %}
    {% spaceless %}
        {% set attr = attr|merge({'class': (attr.class|default('') ~ ' custom-select')|trim}) %}
        <select {{ block('widget_attributes') }}{% if multiple %} multiple="multiple"{% endif %}>
            {% if empty_value is not none %}
                <option value=""{% if required and value is empty %} selected="selected"{% endif %}>{{ empty_value|trans({}, translation_domain) }}</option>
            {% endif %}
            {% if preferred_choices|length > 0 %}
                {% set options = preferred_choices %}
                {{ block('widget_choice_options') }}
                {% if choices|length > 0 and separator is not none %}
                    <option disabled="disabled">{{ separator }}</option>
                {% endif %}
            {% endif %}
            {% set options = choices %}
            {{ block('widget_choice_options') }}
        </select>
    {% endspaceless %}
{% endblock %}

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class YourFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('your_field', ChoiceType::class, [
            'choices' => [
                'Option 1' => 'option1',
                'Option 2' => 'option2',
                'Option 3' => 'option3',
            ],
            'attr' => [
                'class' => 'custom-select',
            ],
        ]);
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'attr' => [
                'class' => 'your-form-class',
            ],
            'block_prefix' => 'your_form',
            'compound' => false,
        ]);
    }
}

{{ form_start(form) }}
    {{ form_widget(form.your_field) }}
{{ form_end(form) }}