let xspeed = 10;

​

function setup() {

  createCanvas(windowWidth, windowHeight);

}

​

function draw() {

  // Background is black with opacity of 15

  // Opacity ranges between 0 and 255

  background(0, 15);

  // Fill color is white with opacity of 127

  fill(255, 127);

  strokeWeight(10);

  // Stroke color is blue with opacity of 50

  stroke(21, 87, 255, 50);

  ellipse(xpos, height / 2, 100, 100);

  // Try changing the increment value below

  xpos += xspeed;

  if(xpos < 0 || xpos > width){

    xspeed = -xspeed;

  }

}

​

function windowResized() {

  resizeCanvas(windowWidth, windowHeight);

}