What variable is modified to change the size of the rectangles in the blinking rectangles challenge?

In the context of the blinking rectangles challenge, the variable that is typically modified to change the size of the rectangles is RECT_LENGTH. This variable generally defines how long the rectangles will be in length, directly influencing their size on the screen.

By adjusting RECT_LENGTH, you can make the rectangles appear longer or shorter, which affects their overall dimensions. While other variables like RECT_WIDTH could also influence the size if it were being modified, in this case, RECT_LENGTH is specifically identified as the variable responsible for changing the size related to the challenge's requirements.

Understanding that RECT_LENGTH controls the length of the rectangles is crucial for manipulating the visual aspects of the animation effectively, allowing for the creation of different visual effects and layouts in the project.