Bootstrap
The most popular HTML, CSS, and JavaScript framework for responsive, mobile-first projects.
Language: CSSCategory: StylingFirst released: 2011Created by: Mark Otto & Jacob ThorntonLicense: MIT
Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS- and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components. Bootstrap is one of the most starred projects on GitHub and has been instrumental in standardizing modern web design patterns with its grid system and component library.
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Key Features
Responsive 12-column grid system with breakpointsPre-built components (navbar, modal, carousel, cards)CSS custom properties for theming and dark modeUtility classes for spacing, display, text, and flexboxSass-based architecture for customizationJavaScript plugins (dropdowns, tooltips, toasts)Extensive form controls and validation stylesRTL support and accessibility features (ARIA)