Custom CSS

I read this post (http://ww.wp.xz.cn/support/topic/plugin-wp-help-modify-css), and I’m not a coder, so I don’t get how to apply customs CSS styles to all my help docs so that they’re synced across all my clients. Help me out. Thanks! LOVE THIS!

http://ww.wp.xz.cn/extend/plugins/wp-help/