HTML 4.01 is the most recent HTML standard. It includes some subtle but significant changes from HTML 4.0. While HTML 4.0 supported Cascading Style Sheets (CSS), HTML 4.01 recommends that they be used to the exclusion of other formatting methods whenever possible. The reason it is only a recommendation is that to require it would cease to allow backwards compatibility of new pages. This means they would not be properly viewable on older browsers.
This latest version of HTML is also called XHTML, which stands for eXtensible HyperText Markup Language.
"Yes, ... I was able to totally change the look and feel of my whole web site, by linking in some new styling features, ... You just can't believe how much fun it is!"