sketch.js

function setup() {
  createCanvas(400,400);
}

function draw(){
  background(255);

  stroke('black');
  strokeWeight(1);
  fill(200, 0, 0);
  circle(200, 200, 150);

  stroke(0);
  strokeWeight(5);
  fill('rgba(100, 200, 100, 0.5)');
  circle(250, 250, 50);
}