Aquarium⁴

Make an interactive aquarium as a single self-contained HTML file. Fill the tank with a mix of fish that swim naturally, some in a school, with rising bubbles, swaying plants, light rippling down from the surface and sand along the bottom. Clicking or tapping drops food that the fish notice, chase and eat. Add a few simple controls: add a fish, feed, and switch between day and night. Draw everything in code, with no libraries or image files, and make it run smoothly on a computer and a phone.