This property controls the color of the left border of an element’s rendering box. If no border-color is specified for an element’s border, the value of the ‘color’ property is used instead.

div { border-left-color: green }

this is green

Possible Values
Value Description
inherit Explicitly sets the value of this property to that of the parent.
transparent The border is transparent (with any accompanying ‘border-width' thickness) - eg: elements below it shine through.
[color] Sets the border to the indicated color value.