and, here's a few things CSS doesn't know…
- Viewport: window/visual-viewport dimensions as px, scrollbar width
- Scrolling: scroll velocity
- Pointer: global pointer position, element-local pointer position
- Element geometry: size as px
- Element visibility: intersection visibility / ratio
- Form controls: range/slider value, generic field value, field state (focus/valid/dirty), form state, select value, color-input value
- Device sensors: device motion, geolocation
- Hardware & system: battery, CPU pressure, FPS, plus head-time constants (CPU cores, device memory, DPR)
- Network & connectivity: online/offline, connection info (effective type/downlink/RTT), navigation type
- Page lifecycle: page focused, page visible
- Time: clock
- Color extraction: image colors, video colors