I don't think there is utf8 characters that allow for drawing on the outside of the cell, (happy to be wrong)

┌ (U+250C), ┐ (U+2510), └ (U+2514), ┘ (U+2518) <-- these 4 draw in the middle of the cell.

｢ (U+FF62), ⌟, (U+231F), <-- these are two that cover part of the outside, but not the other corners.

｢┐└｣

Can anyone tells me how to get those 'corner of cell' characters, including uprights and horizontals ?