/usr/share/plank/themes/Transparent/dock.theme is in libplank-common 0.11.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | [PlankTheme]
TopRoundness=0
BottomRoundness=0
LineWidth=0
[PlankDockTheme]
TopPadding=-12
BottomPadding=2
|