.css File — Cascading Style Sheets

CSS (Cascading Style Sheets) is the style sheet language used to describe the presentation of HTML and XML documents, controlling layout, colors, fonts, spacing, animations, and responsive design. Created by Håkon Wium Lie and Bert Bos in 1996, CSS separates content (HTML) from presentation, enabling consistent styling across multiple pages and easier maintenance. CSS uses selectors to target HTML elements and applies declarations of property-value pairs. Modern CSS (CSS3+) supports flexbox and grid layout systems, custom properties (variables), media queries for responsive design, animations and transitions, transforms, filters, blend modes, shapes, and container queries. CSS has evolved from simple text styling to a powerful layout and animation system that can create complex visual effects without JavaScript. The cascade, specificity, and inheritance rules determine how conflicting styles are resolved. CSS preprocessors (Sass, Less) and utility-first frameworks (Tailwind CSS) have extended CSS workflows, while CSS-in-JS solutions integrate styling with component architectures. CSS Houdini provides low-level APIs for extending CSS capabilities programmatically.