I declared a sundress and ballet flats the hero uniform of my 20s years ago. Now, I'm 24 and rarely wear anything else in the summer. My favorite fashion girls suggest I'll keep styling it well into my 30s, too. On May 28, Barbara Palvin (32) sampled my trusty two-piece in a little black maternity dress and matching Mary Janes. I already added the set to my mom-to-be mood board. For her first outing since her pregnancy style took over the 2026 Cannes Film Festival , Palvin delivered her easiest outfit to emulate all month. (I don't exactly have access to a custom Miu Miu gown yet.) She braved the Hollywood heat in what appears to be a maternity puff-sleeve midi dress from Old Navy . It still being shoppable isn't even the best part. The adjustable, empire waistline style is on-sale for $10.97. Palvin's LBD might be the most wallet-friendly piece I've seen on the entire 2026 celebrity street style scene.…