createCanvas(255, 255); // Set canvas size to 255 by 255 pixels.

  noStroke(); // Disable the drawing of outlines around shapes.

}

​

function draw() {

  background(255, 10); // White background with an alpha transparency.

  let oscillation = map(sin(frameCount / 100), 0, 1, 0, 255);

  fill(oscillation, 0, 255 - oscillation);  // The fill color of the circle.

  circle(mouseX, mouseY, oscillation); // Draw the circle at mouse position.

}