You can carefully inspect the demo for this project and figure out exactly
how to complete this project. Here are the basic requirements:
Create four balls. Each ball should be a different color and each ball
should have two costumes as shown in the demo.
Your background should be very similar to the one shown in the demo
although the exact dimensions of your background may vary slightly from the
one shown in the demo.
Two of your balls should start by moving upward and two of your balls
should start by moving downward. In other words, two of the balls will
appear to always be moving in the opposite direction of the other two
balls.
Make all four balls move at the same speed.
Be careful to space out your balls evenly across the width of the
screen.