That's probably because of the border-collapse property*; this basically
means that the table's border is merged with the outer cells' borders.
Try this, for example:
.viewer table {
border: 2px solid #000;
border-collapse: separate;
border-spacing: 0;
-moz-border-radius: 5px;
}
Just for the record, the "-moz-border-radius" works only on Gecko-based
browsers (like Firefox).
HTH.
-- F.
* http://www.w3.org/TR/CSS21/tables.html#propdef-border-collapse