How to make a message appear once email is submitted using React and CSS

I am using React and have built an email form. I currently have this class: <div className="msg">Message has been sent</div> but only want it to appear when the message has successfully sent. So only when the following resolves as status: true. How can I target this using only React/CSS?

  .post('/api/email', values)
  .then((res) => {
    console.log("Server responded")
    setValues({
      name: "",
      email: "",
      message: "",
      status: true
    })
    .catch(err => {
      console.log(err);
      window.alert("Email not sent")
    });```