Getting rid of the postbit bottom border

It's a bit irritating, isn't it ... the extra-thick line between posts in a thread, resulting from the touching borders of the posts.

I've been desperately trying to get rid of the bottom line of the postbit using style modifiers, for instance ...

style="border-collapse:collapse; border-bottom-width: 0"

in the table tag, and

style="border-bottom-style: none; border-bottom-width: medium"

in the cell (td) tag. Nope ... doesn't work, even though it works in experimental hand-coded HTML pages I've created.

I don't want to split posts apart, like so many people do. I want the threads to be displayed vB style, but with the more elegant UBB single line between posts. Can this be accomplished?