html {
    background-color: silver;
}

body {
    max-width: 50em;
    margin: auto;
    background-color: white;
    padding: 2em;
    border-left: 5px solid grey;
    border-right: 2px solid grey;
}

.example > .example {
    border-left: 1px solid grey;
    padding-left: 1em;
}

.float-caption {
    border-left: 1em solid lightgrey;
    border-bottom: 2px solid grey;
    margin-bottom: 6ex;
    padding-left: 1em;
}

dd {
    border-left: 1em solid lightgrey;
    border-bottom: 2px solid lightgrey;
    margin-left: 1em;
    padding-left: 1em;
}