Lungo2.0.js/examples/kitchen-sink/assets/stylesheets/app.css

pre {
    font-weight: normal;
    font-size: 12px;
    background: rgba(255,255,255,0.5);
    border: 1px solid rgba(0,0,0,0.5);
    margin-top: 10px;
    padding: 10px;
}