title: flutter - how to create forms in popup
body: <p>I want to create a form inside a pop-up with flutter like the image below:
  popup</p>
  
  <p><img src="https://www.formget.com/wp-content/uploads/2014/05/jquery-popup-contact-form.png" alt="popup">.</p>
  
  <p>how can I do that with flutter?</p>