img { max-width: 100%; }

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

html{
    font-size:12pt;
}

@media (min-width: 640px) {
    html {font-size: 16pt;}
}

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