pre {
  background: #303030;
  color: #f1f1f1;
  padding: 10px 16px;
  border-radius: 2px;
  border-top: 4px solid #dd0303;
  -moz-box-shadow: inset 0 0 10px #000;
  box-shadow: inset 0 0 10px #000;
  counter-reset: line;
}

pre span {
  display: block;
  line-height: 1.5rem;
}

pre span:before {
  counter-increment: line;
  content: counter(line);
  display: inline-block;
  border-right: 1px solid #ddd;
  padding: 0 .5em;
  margin-right: .5em;
  color: #888;
  width: 30px;
}