H&M Smocked Off-the-Shoulder Top This UO Step Sister Ribbed Cropped Cami ($20 ... Out From Under Gigi Lace Trim Bra Top Wear this Topshop Laundered Buckle Detail Crop Blouse ($55) with jeans.

Under Armour 25th Anniversary Crop Short Sleeve This Under Armour HeatGear Crop Mock Neck Top ($40) has long sleeves, but the light, sweat-wicking fabric will keep you cool during tough workouts.

You can find her bylines across more than 20 publications. When crop tops and belly shirts skyrocketed ... "Usually, they stay and you do not need to secure them under a bra," Stein adds.

But most importantly, there's a new addition to the lineup: the white, long-sleeved crop top you see above, with rainbow-colored envelopes and "US MAIL" written down the arms, all for just $20.