pre {
white-space: pre-wrap; /* css-3 */
white-space: -moz-pre-wrap !important; /* Mozilla, since 1999 */
white-space: -pre-wrap; /* Opera 4-6 */
white-space: -o-pre-wrap; /* Opera 7 */
word-wrap: break-word; /* Internet Explorer 5.5+ */
}

http://labnol.blogspot.com/2006/10/html-css-trick-for-displaying-code.html

The  tag that defines preformatted text is the only tag in HTML that respects and preserves whitespaces like line-breaks, blanks, tabs and multiple spaces between words. Whatever is enclosed inside the pre element will be displayed as-it-is on the web browser.

Displaying Code Snippets: Wrap Long Lines with PRE Tag

CSS