Audio Cascade Sheets (ACS) is a genuinely novel idea: apply the mental model of CSS — selectors, cascade, inheritance — to sound design for web interfaces. Where a CSS rule says button:hover { color: red }, an ACS rule says how that same element should sound when interacted with, using properties like sound, volume, pitch, and room.

The project ships a runtime you drop into any web page, a <link rel="audiostyle"> tag to reference your .acs file, and 49 built-in sound presets. The landing page eats its own dog food — it is itself an ACS-styled page, so you experience the system as you read about it.

This is firmly a developer tool and a proof-of-concept at the early stage — there is no no-code interface, no visual editor. But the idea is smart: UI sound design is almost universally handled with ad hoc JavaScript, and a declarative alternative with browser-native cascade semantics would be a real improvement. Free and open in spirit, worth watching.