p#intro {
    width:20em;
    margin:auto;
}

main {
    display:flex;
    flex-wrap:wrap;
    justify-content:center;
}

main>div {
    display:flex;
    flex-direction:column;
    align-items: flex-end;
}

main>pre {
    flex:2;
    background-color:#111;
    color:yellow;
    padding:1em;
    margin-left:1em;
    white-space: pre-wrap;
}

main button {
    display:block;
    margin:1ex 0;
    border:1px solid #000;
    padding:1ex;
}

main button.selected {
    background-color:#cfc;
}

footer {
    text-align:center;
    margin-top:3em
}