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 div {width: 50%}
}