.border adds a border on all sides, .border-top, -end, -bottom and -start add one side, and a -0 suffix (.border-end-0) removes a side. .border-1 to .border-5 set the width; the color classes of Colors and Dark Mode (.border-danger, .border-success-subtle) and .border-opacity-50 set the color, but draw nothing without .border. .rounded-0 to .rounded-5 set the corner radius, .rounded-circle and .rounded-pill make circles and capsules, and .rounded-top or .rounded-start-3 round one side.