What is bootstrap framework?

[gautamsharma]

It has pre defined classes to responsive design.

[lishmalinyjames]

Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development.

[Akshay_M]

Bootstrap is a framework designed for front end development to crate modern and responsive websites. Bootstrap is an open-source Javascript framework developed by the team at Twitter. It is a combination of HTML, CSS, and Javascript code designed to help build user interface components.