@media (max-width: 768px) {
  .sb-main-section {   /* This may need adjusting */
    background-image: url("https://theworld.secure.simplybook.it/uploads/theworld/image_files/preview/7f4fc19eb6bbe3b362d1d98ca7a5b710.png?ch=4695?rr=7860");
    background-size: cover;
    background-position: center;
  }
}