The file lib/styles/style.css is missing the definition of the co0 class. This result in no highlighting of comments in e.g. bash-code.
<code bash>
# comment <-- this line is not syntax highlighted
</code>
To set the same style as on the GeSHi demo site (
http://qbnz.com/highlighter/examples.php?c=bash&e=inputrc ):
.code .co0 { color: #666666; font-style: italic; }