The crop top and pencil skirt combo is hot right now and I think this incorporates the 2 in a great way. The long skirt makes it look classy and prevents there being too much revealed skin, which can be easily done with a crop top.
A shift dress hangs loose off the shoulders & has very little to no definition of a waist. Shift dresses are usually at knee-length with a high or boat neckline. The silhouette is primarily from the during the mod period.