SOURCE

let x = 30
let y = 30
let d = 50
let speed = 4
let speed2 = 5
function setup() {
    createCanvas(500, 500)
    noStroke()
    colorMode(HSB, 100, 100)
}
function draw() {
    background(50, 100, 100)
    x += speed
    if ((x > 495 - d / 2) || (x < d / 2)) {
        speed = -speed
    }
    y += speed2
    if ((y > 495 - d / 2) || (y < d / 2)) {
        speed2 = -speed2
    }
    fill(30, 100, 100)
    ellipse(x, y, d, d)
}