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%;
    }
}