This document discusses Cascading Style Sheets (CSS). CSS is a style language that specifies layout of HTML documents. It allows separation of page structure (HTML) from page presentation (CSS). CSS offers formatting elements and ability to control layout from a single style sheet. CSS syntax uses selectors to target HTML elements and properties to set values. There are three CSS styles - inline within HTML tags, internal within <style> tags in <head>, and external in a .css file linked via <link> tag.