XSLT/CSS border style specifications

How does one control the specifications for the various border
    styles for tables, etc. I know how to select the line styles -
    solid, dashed, double, groove, etc - but can the specific metrics
    for each of these be defined? I want to modify the line widths and
    spacing between lines for the 'double' style. (I can specify the
    overall width of line, but is there any finer metrics?) I can't find
    anything in the XSLT specification, apart from the fact that CSS
    properties apply. nor is there anything in the DB stylesheets. I'd
    like to know if this is possible for FO and HTML output.

    Thanks,

    
-- 

      Dave Gardiner