document.addEventListener('DOMContentLoaded', function() {
  var demoForm = document.getElementById('demo-form');
  demoForm.addEventListener('tinyforms:submitted', function() {
    var demoFields = document.getElementById('demo-fields');
    var demoSucess = document.getElementById('demo-success');
    demoFields.style.display = 'none';
    demoSucess.style.display = 'block';
  });
});