Light through a window, built from CSS layers
A dark room lit through a window. Move the pointer and the perspective, the layer parallax and the frame's shadow shift with it. It is CSS the whole way down, apart from the sky outside.
A still scene with the pointer parked reads as a screenshot, so a noise function nudges the layers every 800ms, summing sine waves at unrelated frequencies so the drift never repeats. Reduced motion skips it entirely.