Make one UI component in a single web page: a light/dark toggle switch where the knob is a blob of ferrofluid. The switch is a wide pill sunk into the page. The knob is a glossy blob of black magnetic liquid sitting in the track. In light mode it rests as a smooth droplet that wobbles a little. Click, tap or drag it and it stretches, sloshes and flows to the other end like a real liquid, overshoots a touch and settles. In dark mode a magnet wakes up under that end of the track: the blob rises into sharp ferrofluid spikes that ripple and lean toward the cursor, and the whole page turns dark around it. Switching back, the spikes melt into a smooth droplet again. It should feel physical and look like a finished product, not a demo: real reflections on the liquid, soft shadows, and a soft click and slosh sound made in code. Make everything in code (WebGL or canvas, no image files, no libraries, no image or video models). Put everything in one self-contained index.html with no network requests. It has to work with mouse, touch and keyboard (space or enter). Test it in a headless browser, including toggling it several times and dragging the knob, before you finish.