If you are using Firefox, please see http://meta.askubuntu.com/a/6817/25656 but the code to put into userContent.css would be something like this (assuming you're starting with a blank file):@namespace html url(http://www.w3.org/1999/xhtml);
@-moz-document domain(askubuntu.com)
{
code { font-family: monospace !important; color: purple !important; background: #999 !important; }
}