The border-bottom shorthand property sets border-bottom-width and/or border-bottom-style and/or border-bottom-color to the bottom side of an element simultaneously.
The border-bottom CSS property sets the width, style, and color of the bottom border of an element. It is a shorthand property for setting the individual bottom border properties i.e. border-bottom-width, border-bottom-style, and border-bottom-color at once
The syntax of the property is given with:
border-bottom: |
[ border-bottom-width border-bottom-style border-bottom-color ] | initial | inherit |