It's such a general description, the modernist version of sleek navy suit with little detailing and no apparent texture, no belt, simple black shoes or boots and plain white shirt with little detailing and no apparent texture is still A-OK. The "look I'm cool I don't wear a tie but everything else looks like regular suit-guy wear" was never ok.
This. It is as much confidence and an eye for cohesive fit as anything. Our elected officials often elect to offend even awfully overt aesthetic commandments, e.g. the poorest fitting jacket possible. But when fit, proportion, and details are checked accordingly, it is seemingly an always-in-style getup.