body {
  margin: 0;
  padding: 0;
  background-color: antiquewhite;
}

#main {
  position: relative;
}

#theme {
  position: absolute;
  top: 10px;
  right: 10px;
}

canvas {
  display: block;
}

#sketch {
  width: 400px;
  height: 400px;

  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;

  margin: auto;
}