Compare with Bootstrap 3, Bootstrap 4 has added many new functions and made some changes. Flex box is one of the new functions. According to the course instructor, flex box includes a bunch of CSSA properties to move things around the position elements inside of a container instead of a page. Basically, flex box is a model for positioning content inside a box. Let's see some flex box examples. Bootstrap 4 has a new starter template which includes the latest design and development standards. Therefore, I just copy the HTML template on my code editor. Then, I create two buttons inside a container and add a border to the container. This will help you to see how those buttons move inside the box. Justify-Content (Move in Row) To make two buttons move to the left in the flex box, we need to add a property value: "d-flex" . It means "display flex", and it will help to set the directions. For the default value, the items are on the left. The ...