This document introduces CSS (Cascading Style Sheets) and provides an overview of some basic CSS concepts: - CSS allows authors to define styles that can be applied consistently throughout a project for formatting elements like headings, paragraphs, etc. This improves efficiency and consistency compared to local formatting. - A style sheet is a separate file containing all styles for a project. It cascades in that changes can inherit to child styles. - The document discusses CSS basics like style rules, the box model, relative sizing units, and different CSS levels. - It recommends best practices like defining styles upfront in a CSS before authoring and avoiding inline styles.