There is a specific dress for sunny afternoons in parks and gardens. You know the one. Floaty, cheerful, easy to sit on a blanket in, looks good in the photos someone takes while you’re pretending not to notice. We’ve assembled what we think is a brilliant collection of picnic dresses. The kind that work with flat sandals or espadrilles, that don’t wrinkle the moment you sit down, and that have that summery ease that makes a casual day feel like a proper occasion.