main {
    margin: 10px;
    display: flex;
    flex-flow: row wrap;
    justify-content: space-around;
}

  main a {
    min-width: 170px;
    max-width: 500px;
    width: auto;
    height: auto;
  }

    img {
      border: 3px solid black;
      width: 100%;
      margin: 1px;
      height: auto;
    }