✓ 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 is top (air) which is correct conceptually but the writing-mode/rtl CSS makes the physical drag direction opposite to expectation (dragging down increases value, but visually the thumb moves up due to `direction: rtl`), causing UX confusion; all physics, visuals, and Heureka animation are otherwise well-executed.
Slider direction is inverted — value=0 is top (air) which is correct conceptually but the writing-mode/rtl CSS makes the physical drag direction opposite to expectation (dragging down increases value, but visually the thumb moves up due to `direction: rtl`), causing UX confusion; all physics, visuals, and Heureka animation are otherwise well-executed.