If the line style for a border is double, use the border line properties style:border-linewidth, style:border-line-width-top, style:border-line-width-bottom, style:border-line-width-left and style:border-line-width-right to individually specify the width of the inner and outer lines and the distance between them.

The style:border-line-width specifies the line widths of all four sides, while the other attributes specify the line widths of one side only. The value of the attributes can be a list of three space-separated lengths, as follows:

The first value specifies the width of the inner line

The second value specified the distance between the two lines

The third value specifies the width of the outer line