The border-bottom-color property sets the color of an element's bottom border.
The border-bottom-color CSS property sets the color of an element's bottom border individually. However in many cases the shorthand CSS properties like border-color or border-bottom are more convenient to use and preferable.
Always declare the border-style or the border-bottom-style property before the border-bottom-color property. An element must have a border before you can change the color.
border-bottom-color: color|transparent|initial|inherit;