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%;}
}