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%}
}