当Formik窗体isSubmitting时，如何向按钮添加类？

import { Formik, Form, Field, ErrorMessage } from 'formik';

const MyForm = () => {
  return (
    <Formik
      initialValues={{ name: '' }}
      onSubmit={(values, { setSubmitting }) => {
        setTimeout(() => {
          alert(JSON.stringify(values, null, 2));
          setSubmitting(false);
        }, 400);
      }}
    >
      {({ isSubmitting }) => (
        <Form>
          <Field type="text" name="name" />
          <ErrorMessage name="name" component="div" />
          <button
            type="submit"
            className={`btn ${isSubmitting ? 'submitting' : ''}`}
            disabled={isSubmitting}
          >
            Submit
          </button>
        </Form>
      )}
    </Formik>
  );
};

export default MyForm;