Light gray outlines are shown for reference.
All breakpoints
.baborder all sides.btborder top.brborder right.bbborder bottom.bl border leftLarger than mobile breakpoint
.ba-ns border on all sides for breakpoints larger than mobile.br-ns border on right for breakpoints larger than mobile.bb-ns border on bottom for breakpoints larger than mobile.bl-ns border on left side for breakpoints larger than mobileMedium breakpoint
.ba-m border on all sides for medium sized breakpoint.bt-m border on top side for medium sized breakpoint.bb-m border on bottom side for medium sized breakpoint.bl-m border on left side for medium sized breakpointDesktop and larger
.ba-l border on all sides for large sized breakpoint.bt-l border on top side for large sized breakpoint.br-l border on right side for large size breakpoint.bl-l border on left side for large breakpoint