Note sure what your wanting to do. If your wanting to modify the lastpost area add the following in extra.css and adjust accordingly.
Are you wanting the dotted border around the lastpost area?
Not sure this is what your looking for but try the following (I'm sure it can be done via style properties) and/or add that to EXTRA
Edit: I vaguely remember having a similar issue before but it had nothing to do with the quotes if your referring to the slightly more white above the signature border.