1990s: Shaded, semi-realistic
2010s: Material design. No shading. Simple designs.
2020s: Flatter designs. Low information icons.
2030s: Icons are now variations on circles, squares, and triangles, which are invisible.
@craigmaloney What about the GLOSS?
@Jookia Ah, right. The lickable interfaces. Forgot to put that into the 1990s / 2000s.