body {
  background-color: #376482;
  height: 100vh;
  overflow: hidden;
  display: flex;
  justify-content: center;
  align-items: center;
}

.snowball {
  position: absolute;
  cursor: pointer; 
  width: 640px;
  height: 480px;  
}

.snowball:after {
  content: "";
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  background: url(https://noel-rgpd.jeeve.eu/images/snowball-2.png) center center / contain no-repeat;
  z-index: 10;
}

canvas {
  position: absolute;
  margin:0;
  width: 640px;
  height: 480px; 
}