Please change

  code {
    font-family: 'DejaVu Sans Mono';
  }

in your CSS to

  code {
    font-family: 'DejaVu Sans Mono', monospace;
  }

For people without DejaVu Sans Mono installed (or for browsers doing a good job at defeating font fingerprinting), which would be most people, the code sample is rendered in the default proportional font, which is very ugly.