body {
    margin: 0 auto;
    padding: 2em;
    max-width: 50em;
    font-size: 18px;
    font-family: sans-serif;
}
main {
    box-sizing: border-box;
    padding: 0 15px;
    margin 0;
}
footer {
    margin-top: 2em;
}
pre {
    overflow: auto;
}
code {
    overflow: auto;
}