The border-left-width property sets the left border width of an element. Note: the Border Style property must be set for any of the other border properties to work.
Value
Description
(numeric)
e.g. '15' would set the left border for an element to 15 pixels (Microthemer automatically adds the 'px' unit if a unit isn't specified). Other commonly used units include 'em' and '%'. So you could enter '5%' in the Left Border Width field.
Border Left Width
The border-left-width property sets the left border width of an element. Note: the Border Style property must be set for any of the other border properties to work.
Themeover CSS Reference
Online CSS References: Border Left Width
Online CSS Tutorials: Border