.iframe-container iframe {
  width: 100%;
  height: 80vh; /* importante para forms */
  border: none;
}

.image-cover {
  width: 100%;
  height: 100%;
  min-height: 500px; /* garante presença */
  background-image: url("/img/join.jpg");
  background-size: cover;
  background-position: center;
}