CSS

A CSS rule picks elements with a selector and sets properties on them, such as making every link blue or laying out a product list as a grid. 'Cascading' describes how the browser settles conflicts when several rules apply: the more specific rule wins, and among equals the later one. That cascade is powerful, and also the usual reason a style mysteriously refuses to apply.

Modern CSS handles work that once needed JavaScript or add-on tools: Flexbox and Grid for layout, media and container queries for responsive design, custom properties (variables), nesting, the :has() selector, transitions and animations. Other tools build on CSS rather than replace it: Sass adds extra syntax, and Tailwind CSS generates small utility classes that you combine in the HTML.