Posting source code.

I found this link http://faq.wordpress.com/2007/09/03/how-do-i-post-source-code/ for posting code.

I have tried to do it in my blog with no success.

[sourcecode language='css']
#commentlist li {
margin: 10px 0 0;
padding: 10px 10px 5px;
list-style: none;
}
[/sourceode]

I am using K2 as my theme, could this effect it?

thanks