CSS BORDER-COLOR

This is a shorthand property which allows an author to specify ‘border-top-color’, ‘border-right-color’, ‘border-bottom-color’, and ‘border-left-color’ properties using a single property and value notation (the values are given in this order separated by spaces.) If one or more of the values are not present, the value for a missing side is taken from the opposite side that is present. If only one value is listed, it applies to all sides. If no border-color is specified for an element’s border, the value of the ‘color’ property is used instead.

Example
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em { border-color: blue } 
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<em style="border-color: #ff0000 green">This is an Emphasized Test</em>

Possible Values

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.