Border
Bootstrap includes border utilities to quickly style the border and border-radius of an element. Great for images, buttons, or any other element.
To understand in more detail review the following documentation: Bootstrap Border.
Border placement
border-top
border-end
border-bottom
border-start
Border color
border-primary
border-secondary
border-success
border-info
border-warning
border-danger
border-light
border-dark
Border radius
rounded
rounded-top
rounded-end
rounded-bottom
rounded-start
rounded-circle
rounded-pill
rounded-0
Border radius size
rounded 0px - 0rem
rounded 8px - 0.5rem
rounded 16px - 1rem
rounded 24px - 1.5rem
rounded 32px - 2rem
rounded 40px - 2.5rem
rounded 50% - 50rem