Bottom Element (BorderWidth) (RDL)
Specifies the width of the bottom border of the item.
Bottom contains an expression that evaluates to a string that contains a number (with a period character used as an optional decimal separator). The number must be followed by a designator for a CSS length unit such as cm, mm, in, pt, or pc. A space between the number and the designator is optional. For more information about size designators, see "CSS Length Units Reference" at msdn.microsoft.com.
The value for the Bottom element must be between .25pt and 20pt.