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;
    }
    h1{
        font-size:2.5rem;
    }
    .two-columns-example{
        display: flex;
    }
    .two-columns-example > * {
        width: 50%;
    }
}