Following table should have 6px solid blue border around cell 3, red 5px solid border around the rest of table and green 4px solid border between cell 1 and cell 2. The red border should override the green border around the cells because it's thicker and the blue border should override the red border for the same reason.

See 17.6.2 The collapsing border model for following tests:

This is an example rendering for the previous table from http://www.w3.org/TR/REC-CSS2/images/tbl-border-conflict.gif:

Following table should have 2px solid black line between rows. There should be a total of two lines. There will be three lines if user agent doesn't support tr:first-child.