@media only screen and (max-width: 768px) {
  #about .main {
    flex-direction: column-reverse;
    align-items: center;
  }

  #about-text h3 {
    text-align: center;
  }

  #img1 {
    display: none;
  }

  #img2 {
    display: block;
  }
}

@media only screen and (min-width: 769px) {
  #img1 {
    display: block;
  }

  #img2 {
    display: none;
  }
}