Bootstrap 2,007 is a free, MIT-licensed collection of CSS and JavaScript that gives you a responsive grid, styled form controls, navigation bars, modals and hundreds of utility classes. You write ordinary HTML, add class names such as container, row, btn btn-primary or mt-3, and the page looks consistent in every modern browser without a line of custom CSS. That trade (you learn a vocabulary of class names, Bootstrap supplies the design decisions) is why W3Techs 13,241 still finds it on about one website in seven in September 2026.
This chapter comes before the CSS chapter on purpose. You can build a presentable, mobile-friendly page with only basic CSS knowledge, and then CSS explains the selectors, the box model, flexbox and grid that Bootstrap uses internally. Whenever a Bootstrap class maps to a CSS feature worth understanding, the text points you to the relevant section of CSS. Tailwind CSS then shows the utility-first alternative, Tailwind CSS 5,202 .
All examples use Bootstrap 5.3.8, the current stable release, loaded from the jsDelivr 15,886 CDN, and most of them show a screenshot of the result. The last sections look at customizing Bootstrap with Sass 22,539 , the ecosystem of themes and framework ports, and what changes in Bootstrap 6.
What you will learn:
How to install Bootstrap from a CDN or npm 2,036 and how its Sass, CSS variables and plugins fit together
The 12-column responsive grid, containers and breakpoints
Components: buttons, cards, navbars, modals, offcanvas panels, toasts and forms with validation
Utilities for spacing, positioning, colors, borders and display
Customizing and theming Bootstrap, including dark mode, and choosing ecosystem add-ons
Migrating to Bootstrap 6, and building a landing page and an admin dashboard