Build a cozy living aquarium in the browser (single HTML page, no external assets). Original, adorable fish with personalities school, chase each other, nibble plants and sleep at night; bubbles rise, light ripples across the sand, a little treasure chest burps air. Click to drop food and watch them race for it, tap the glass and they scatter, and a Feed, Lights and New Fish button. It should feel calming and alive the moment it loads.