CSS to make an empty cell's border appear?

The question asked for a CSS solution, but on the off-chance an HTML solution will do, here is one:

Try adding these two attributes to the table element: frame="box" rules="all" like this:

 border="1" cellspacing="0" frame="box" rules="all">

http://stackoverflow.com/questions/57002/css-to-make-an-empty-cells-border-appear