Bootstrap, formerly Twitter's Bootstrap, is the most popular HTML, CSS, and JavaScript framework to develop responsive, mobile-first projects on the web. You can use Bootstrap to build responsive websites and applications. This framework helps you to develop faster and more efficient applications using proven CSS code and components.
Bootstrap uses a responsive grid with 12 columns and many other reusable components.
In this chapter, you will learn more about Bootstrap's CSS. Bootstrap 4 is built with LibSass and Grunt. Using Sass as a preprocessor for the CSS code makes Bootstrap's code reusable and extendable. In this chapter, you will learn how to customize and extend Bootstrap by using Sass.