Content, Structure, and Presentation involve various elements like text, images, videos, sounds, animations, and files intended for your audience. XHTML lets you specify the nature of each content element, while CSS empowers you to determine the appearance and presentation of each element to your audience.
The landscape is evolving - widespread adoption of web standards enables designers to create well-organized pages. In the past, the norm was to code everything using tables for page layout. Nowadays, most browsers adhere to XHTML and CSS as the standard.
Creating XHTML involves understanding that CSS is a tool for enhancing the style of HTML. It's important to note that a CSS file relies on an XHTML file; they go hand in hand. XHTML, built on free-form XML, allows for the naming of tags to describe the enclosed content. As an XML-compliant language, XHTML has surpassed the constraints of HTML, positioning itself for future expansion.