Cascading Style Sheets (CSS) is used to format and lay out web documents. CSS works with HTML and JavaScript. CSS uses rules and selectors to style elements by changing properties like colors, sizes, and positioning. A style sheet contains rules with selectors that match HTML tags and attributes. The declaration block then sets property values. Common properties include width, background color, text alignment, and borders. Selectors target elements by type, ID, class, and placement. Examples demonstrate styling navigation bars and clouds. The presentation concludes with a Q&A.