In the Modern and International styles of the 1960s and 1970s where form follows function, the vents' presence is not seen as undesirable. Rather it emphasizes the functional layout of the building by dividing it neatly into equal blocks, mirroring the layout of the elevators and offices inside. This could be clearly seen on the Twin Towers of the World Trade Center and can be seen on the Willis Tower. In the IDS Tower in Minneapolis, the lowest mechanical floor serves as a visual separation from the street- and skyway-level Crystal Court shopping center and the office tower above; the upper mechanical floor (above the 50th and 51st floors, the uppermost occupied floors) serves as a "crown" to the building.