In the book: Advanced DPA Theory and Practice: Towards the Security Limits of Secure Embedded Circuits 1, it is explained that the countermeasures against Side-channel Cryptanalysis could be ensured through 3 levels; Software Level, Hardware Level and the Logic Style Level.
The question is, why the Logic Style, which is defined in 2 as
"the way how logic gate is constructed"
not considered as a part from the Hardware level?
I can't clearly spot the difference, is there some fundamentals that I might be confusing?