discourse/app/assets/stylesheets/mobile/components/welcome-header.scss

.login-welcome-header {
  .login-title {
    font-size: var(--font-up-5);
  }

  .login-subheader {
    font-size: var(--font-0);
  }

  .waving-hand {
    width: 30px;
    height: 30px;
  }
}