This feature is currently available in TreeHouse build 20130701, and will soon be released to all registered users of HTML-Kit Tools. You can keep an eye out for it using "Help > Check for Updates" menu option.
If you're working with not so tidy CSS files, you can now get them to look great with a single click.
Simply open a *.css file and click Beautify CSS link on the bottom. You can reformat specific CSS blocks by selecting them before using this feature. As shown in the video, even minified CSS can be made readable.