Hold space to control the focal point without manually moving slider at the top. Press 3 to control cat 3's size, press 2 to control cat 2's size and press 1 to control cat 1's size by moving your mouse. You can also drag the cats. In this version, you can click a cat and the computer will automatically focus in this area, kind of like single auto focus in a camera
Other version: https://scratch.mit.edu/projects/1233702134/