This document provides an introduction to Cascading Style Sheets (CSS) including what CSS is, its syntax and structure, and the different types of CSS including external, internal, and inline styles. CSS was created in 1996 to separate document structure (HTML) from presentation (styles). CSS uses selectors to apply declarations blocks containing property-value pairs that define elements' styles. External styles are ideal for consistency across pages while internal and inline styles are for one-off or unique styling. The cascade order determines which styles take precedence. Advantages of CSS include separation of concerns, easier maintenance, faster pages, and compatibility across devices.