marble floor and dark wood look good together. But the lack of a DW wall is an issue.
The marble arch is the only piece with that cutout and it does not fit well as an arch. Its occasionally handy as a shelf or cut out to stick a tub through (to vent it outside) or the like.

The best look for the marble arch may be to embed a 1x1 that will obscure the cutout.
It also is sort of OK if its a hanging arch (arches, one of their good points is they glue to a wall without under support).

The darkwood arch/door looks really nice in marble. Its an easy, nice looking alternative:
https://steamcommunity.com/sharedfiles/filedetails/?id=2956212661

this is tricky. I have no mods, and it took me a couple min to get it to go. It finally went by getting the mouse in just the right spot, as you can see.
https://steamcommunity.com/sharedfiles/filedetails/?id=2956212668

I trust you can hang a pair with nothing under them and judge for yourself if that has merits. Its sort of clunky, but it may be ok if done carefully with the angled wall pieces to make an oddball entry or something.