@media (max-width: 500px) {
  body div.webform-confirmation-modal {
    width: 300px !important;
    margin: 0 10px !important;
  }
}
@media (min-width: 501px) {
  body div.webform-confirmation-modal {
    width: 450px !important;
  }
}
@media (min-width: 800px) {
  body div.webform-confirmation-modal {
    width: 600px !important;
  }
}