✓ 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 (hint says "pull up to submerge" but range input with writing-mode vertical-lr/rtl maps value=0 at bottom and value=100 at top, making top=air/bottom=water — the label/hint is confusing and the directional convention is non-standard); otherwise the demo is polished, physics-correct, and feature-complete with a well-executed Heureka overlay and live panel values.
Slider direction is inverted (hint says "pull up to submerge" but range input with writing-mode vertical-lr/rtl maps value=0 at bottom and value=100 at top, making top=air/bottom=water — the label/hint is confusing and the directional convention is non-standard); otherwise the demo is polished, physics-correct, and feature-complete with a well-executed Heureka overlay and live panel values.