A black one-shoulder gown can be visually dramatic without using a bright colour. Here the diagonal neckline has a small opening beside the covered shoulder, while reflections continue down the close upper skirt. The lower skirt opens around the leg and spreads into a train. Read these features together when comparing the dress with a wedding brief; the dark background does not make the design understated.
For a guest outfit, first decide whether this much trailing length is appropriate to the event and manageable along the actual route. Try walking and turning in your own shoes before considering accessories. The raised hem at the opening should be checked while seated as well as standing, because the arranged pose shows only one position.
The exposed shoulder leaves room for an earring, but the photograph does not prescribe a particular jewellery size. Try a small option before adding a longer one, and see the neckline with your intended hairstyle. If you need an outer layer for the ceremony, test where its front edge crosses the diagonal detail so that the complete arrival outfit feels deliberate.