[Enhancement] Drop shadow box styling should be changed

[Rubaiyat-E-Mohammad]

Description: In the doc navigation Gutenberg block, there is an option for drop shadow selection. Selecting any drop shadow style is imposing on full width. It should impose style on the individual blocks of "previous document" and "next document." Should not impose the style between both the blocks. Areas between both the blocks should be unchanged.

Screen record:

https://github.com/user-attachments/assets/d6cd7b39-e295-46c0-aa37-8fd4995165e0