img {
    max-width: 100%;
}

body{
    margin-left: auto; margin-right: auto;
    width: 90%;
    max-width: 40rem;

    @media (min-width: 640px){
        .two-columns-example{
            display: flex;
        }
        .two-columns-example > *{
            width: 50%;
        }
    }
}