✓ Two crowns ✓ Same mass, different density ✓ Vertical slider ✓ Slider works ✓ Slider controls crowns — Slider direction correct ✓ Full slider range — Fall animation ✓ Water displacement ✓ Rising water level ✓ Splash effects ✓ Physics correct ✓ Live mass value ✓ Live volume value ✓ Live density value ✓ Live displaced water ✓ Gilded displaces more ✓ Heureka animation ✓ No external deps ✓ Light bg / dark text ✓ Self-contained HTML
Slider direction is inverted (value=0 at top maps to crowns in air, which is correct semantically, but the slider's visual orientation via writing-mode/direction/rtl means dragging up increases value and pushes crowns down into water — needs verification; fall animation is absent as crowns jump instantly with slider rather than animating independently; the HEUREKA pulse uses font-size scaling instead of a transform, and the submerged fraction calculation ignores the rising water surface feedback loop.
Slider direction is inverted (value=0 at top maps to crowns in air, which is correct semantically, but the slider's visual orientation via writing-mode/direction/rtl means dragging up increases value and pushes crowns down into water — needs verification; fall animation is absent as crowns jump instantly with slider rather than animating independently; the HEUREKA pulse uses font-size scaling instead of a transform, and the submerged fraction calculation ignores the rising water surface feedback loop.