body {
  margin: 0;
  padding: 0;
  background: #70c5ce;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

canvas {
  border: 2px solid #000;
  background: #70c5ce;
}
* {
  margin: 0;
  padding: 0;
}
canvas {
  display: block;
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;  /* 100% viewport width */
  height: 100vh; /* 100% viewport height */
}