HTML and CSS Reference
The onMouseClick() function
When the user clicks the mouse on the game screen, this event listener function determines
which of the 25 squares was clicked. It calls the appropriate TextButton instance's
pressDown() function and then its draw() function, passing in the context.
The onMouseMove() function
When the mouse is moved, this event listener function will set the mouseX and mouseY values
to the current mouse position on the canvas.