The Bootstrap 4 is the newest version of Bootstrap , which is the most popular HTML, CSS, and JavaScript framework for developing responsive, mobile-first web sites. The new features are, Bootstrap 4 Source CSS files Converted in SCSS. Bootstrap 4 has 5 grid system ( .col-, .col-sm-3, .col-md-3, .col-lg-3, .col-xl-3 ). Bootstrap 4 has removed the xs from the lowest breakpoint. Therefore, ( col- ) covers all devices. Bootstrap 4 has changed the offset class ( .offset-md-4 ) In Bootstrap 3 we are used this ( .img-responsive ) class for the responsive image. Bootstrap 4 has changed the class for a responsive image ( .img-fluid ). Bootstrap 4 has changed to ( .form-control-lg ) and ( .form-control-sm ) to increase and decrease the input size. To learn more click here .