Bootstrap is the most popular HTML, CSS, and JS framework for developing responsive, mobile first projects on the web.
Mobile first approach: Since Bootstrap 3, the framework consists of Mobile first styles throughout the entire library instead of in separate files.
Browser Support: It is supported by all popular browsers.
Easy to get started : With just the knowledge of HTML and CSS anyone can get started with Bootstrap. Also the Bootstrap official site has a good documentation.
Responsive design : Bootstrap's responsive CSS adjusts to Desktops , Tablets and Mobiles.
Bootstrap is designed for anyone, everywhere enabling front-end web development faster and easier. The Infocom team provides effective assistance and support to design if suitable for people of different skills, devices of varied shapes and projects of any ambience to be comfortable with a single code base, from phone to tablets or desktops or with CSS media queries.