Expected: first table shows double lines between cells (each cell keeps its own 2px border, 4px apart). Second table shows single 2px lines — adjacent borders merge. Third table: the middle cell declares a 6px red border, which must win the conflict against its neighbors' thin grey borders on all four shared edges.
| a | b | c |
| d | e | f |
| a | b | c |
| d | e | f |
| a | b | c |
| d | thick wins | f |
| g | h | i |