CSS

Style sheet language for describing the presentation of documents written in HTML or other markup. Controls typography, colors, spacing, layout, and visual effects while keeping structure separate from appearance.

Maintained as a W3C standard by the CSS Working Group, with specifications developed openly on GitHub. Universal across all modern browsers and supported by every web framework. The working group publishes annual CSS snapshots documenting stable and upcoming modules.

Core features:

• Flexbox and Grid for responsive layouts without floats or hacks
• Custom properties for design tokens and theming
• Media queries for device-specific and responsive design
• Cascade and inheritance for maintainable stylesheets
• Animations and transitions for motion and interaction

Used to style any web application, from static sites to single-page apps. Flexbox and Grid simplify complex layouts, custom properties power design systems, and media queries enable mobile-first responsive UIs. Integrates with build tools like PostCSS and preprocessors such as Sass, or used directly in modern frameworks.