I can't clear canvas on my green screen program

Question

I can not clear canvas, follow the jc code:

function clear() {
  var canvas = document.getElementById("can");
  var canvas2 = document.getElementById("can2");
  var canvas3 = document.getElementById("resultado");
  var ctx = canvas.getContext("2d");
  var ctx2 = canvas2.getContext("2d");
  var ctx3 = canvas3.getContext("2d");
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx2.clearRect(0, 0, canvas2.width, canvas2.height);
  ctx3.clearRect(0, 0, canvas3.width, canvas3.height);
}

codepen link:https://codepen.io/AlissonTelez/pen/NWxJmEY

the button to make green screen is work correctly, but the clear button don't.