Hello,
We have done some tests with some MS Word versions and don't see any way to apply transparency to the outer table. Even after removing the borders, MS Word does an overlapping. Transparency (no color) and z-index can be applied to very specific contents in MS Word.
Maybe the easiest solution is to set a very low value that displays the left corner and move the alignment as little as possible:
'left' => 36,
Cell margins use twips (twentieth of a point) as size value.
Regards.