It should be loosely Art Nouveau inspired and harmonize with Tolkien's design for the Doors of Durin.

Rivendell meanwhile should be not Art Nouveau but Arts and Crafts movement inspired. Lots of surprising detail.

Further unpopular opinon: Khazad'Dum should be a different style or architecture and ornament than The Lonely Mountain though they should share design elements in common and Lothlorien should look basically nothing like Rivendell. Totally different sensibilities, languages, cultural heritage that is not Elrond's very fused but very western family background.

yeah i would LOVE to see some diversity in design elements among the seven dwarf clans!

we got a teeny bit of that in The Hobbit, with the Ri brothers being Broadbeams from the Blue Mountains, but it was more of a class division (craftsman vs the Durin soldiers) than visual differences

Yeah! I mean the founders of The Lonely Mountain were Durin descendents but they were thousands of years out from the building and flourishing of Moria! Time scales like that change cultural tastes.

And you are right about the family stuff too. Lots of cultural difference even in allied and close companions.

whoops i mistyped! the Ris were also Lonely Mountain refugees, it was the Ur bros who were Blue Mountain boys

BUT MY POINT STANDS!

It does!!!