This code creates an SVG element with a default avatar consisting of a gray rectangle and three white circles. Clicking the "Change Avatar" button randomly selects three shapes (either rectangles or circles) and colors them randomly from a list of available colors. The new shapes replace the old ones in the SVG element.
Note that this is just a simple example to get you started. You can modify this code to include more shapes, more colors, and more complex shapes. You can also add additional functionality, such as saving and loading user-generated avatars or allowing users to customize the size and position of the shapes.