What is Valid XHTML and CSS?

All computer languages (such as XHTML and CSS) have their own grammar rules. Poor 'grammar' results in awkward coding that doesn't always work proporly.

Using Valid XHTML and CSS makes sure that all web browsers, operating systems, and visitors can view the same content.

All my web designs are Valid XHTML and CSS and cooperate with W3C's XHTML and CSS standards.