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16 pixels by 16 pixels is a common resolution for assets matching a low-res pixel art aesthetic. Although the assets may not be specifically 16x16, they are designed to work in a graphical setting where objects are around that size.

Sprites are generally 2D images used in games to represent objects. They can be animated or static, and come in different styles like isometric or top-down.

Resources for building and relating to User Interfaces, how the user interacts with your program