@media only screen and (max-width: 640px) {
  .newsletter-next-step-page h3 {
    text-align: center;
  }
  .newsletter-next-step-page .left-container {
    flex: 100%;
  }
  .newsletter-next-step-page .right-container {
    margin-top: 1.5em;
    flex: 100%;
    text-align: center;
  }
}