Socially distant fashion shows are now a thing — note the masks, and the carefully spaced chairs — and it’s nice when the garments fit the theme. Christian Siriano’s Fall 2021 ready-to-wear show, held at New York’s Gotham Hall, ended with this elegantly sculptural garment, with a vast heart-shaped skirt and winglike shoulders. You can’t stand too close to someone wearing this dress — the better to admire it, from a safe distance.