This document provides an introduction and overview of CSS (Cascading Style Sheets). It covers what CSS is, why it is used to separate content from presentation, and its basic syntax and structure. CSS allows separation of HTML content from its visual presentation by defining styles like fonts, colors, and spacing in external CSS files or internal <style> tags that can be applied to elements on the page. The key benefits highlighted are maintenance of presentation separately from content and cascading/inheritance of styles.