CSS, or Cascading Style Sheets, is a language used to control the visual appearance of HTML content in a browser. It defines colors, fonts, layouts, spacing, and how elements respond to different screen sizes. While HTML describes structure, CSS controls presentation and design. Browsers apply CSS rules based on selectors that target elements, classes, or IDs. The cascade determines which rules take priority when multiple styles apply to the same element. CSS enables responsive design so pages can adjust to phones, tablets, or large screens. Modern CSS features allow for animations, grid layouts, and variables that make styling more maintainable. Frontend developers rely heavily on CSS frameworks, but understanding native CSS helps debug issues effectively. When working with AI tools that generate UI, clear CSS constraints improve results.
key characteristics
CSS rules are applied in order of specificity, source, and importance. Layout systems like flexbox and grid provide powerful ways to position elements without manual calculations. Browsers parse CSS and build a render tree that determines how elements appear visually. Performance can be influenced by selector complexity and how often the browser must reflow or repaint. CSS integrates closely with HTML and JavaScript, forming the core of web presentation. Good CSS structure keeps styling modular and consistent, especially in large applications.