Aqua

Jobs unveiled Aqua at Macworld Expo in January 2000, eight months before the Mac OS X public beta. Everything was to look like water: translucent blue buttons, a pulsing default button, pinstriped window backgrounds, soft shadows and a Dock whose icons swelled as the pointer passed over them. The three coloured buttons at top left, close, minimise and zoom, replaced Mac OS 9's boxes, and a minimised window was sucked into the Dock with the genie effect. All of it needed Quartz Compositor; the style was as much a demonstration of the new graphics layer as a design choice.

Aqua has since been peeled back a layer at a time. Brushed metal came and went during the 2000s, the pinstripes vanished with Leopard in 2007, the gel with Yosemite in 2014 and most of the depth with Big Sur in 2020, which borrowed iOS's rounded shapes instead. With macOS Tahoe in 2025 the style was renamed Liquid Glass. Apple nonetheless called the interface Aqua in its guidelines for over two decades, and the traffic lights are still where they were in 2001.