border-t-4 border-red-500
Use
border-t-{width}
for a top border. Color is optional (e.g.,
border-t
for default).
border-b-2 border-indigo-600
Use
border-b-{width}
for a bottom border.
border-x-4 border-lime-500
Use
border-x-{width}
for left and right borders simultaneously.
border-t-2 border-t-pink-500 border-b-4 border-b-cyan-500
You can combine directional borders. For example,
border-y-{width}
for top and bottom, or specify each individually.