CSS3
CSS3 is the current generation of Cascading Style Sheets, the language used to style and lay out web pages, extending earlier CSS with modules for animations, transitions, gradients, flexible layout systems, and responsive design features.
Definition
CSS3 is the current generation of Cascading Style Sheets, the language used to style and lay out web pages, extending earlier CSS with modules for animations, transitions, gradients, flexible layout systems, and responsive design features.
Overview
CSS3 broke from the single, monolithic CSS2 specification by splitting styling capabilities into independent modules — selectors, box model, backgrounds and borders, animations, transforms, and more — each evolving and shipping in browsers at its own pace. This modular approach let browser vendors implement and ship new capabilities like rounded corners, gradients, shadows, and transitions years before a full "CSS3" spec could ever be finalized as one document, which is also why, like HTML5, "CSS3" today mostly functions as an informal era label rather than a single versioned standard. The biggest practical shift CSS3 brought was in layout: Flexbox and later CSS Grid replaced brittle float- and table-based layout hacks with purpose-built one-dimensional and two-dimensional layout systems, making responsive web design dramatically easier to implement. Media queries let styles adapt based on viewport size, device orientation, or user preferences like reduced motion or dark mode, and CSS custom properties (variables) let teams build themeable, maintainable stylesheets without a preprocessor. CSS3's animation and transform modules also made it possible to build smooth, GPU-accelerated interface motion natively, reducing reliance on JavaScript animation libraries for common effects. Preprocessors like SASS and LESS, and tools like PostCSS, grew up around CSS3 to add variables, nesting, and build-time transforms before native CSS caught up on some of those features, and frameworks built on top of CSS3 (utility-first systems in particular) remain a fast, common way teams style modern apps.
Key Features
- Modular specification covering selectors, layout, animation, and more independently
- Flexbox and CSS Grid for modern one- and two-dimensional layouts
- Media queries for responsive, condition-based styling
- Native transitions, animations, and transforms
- Custom properties (CSS variables) for themeable stylesheets
- Gradients, shadows, and rounded corners without images