html,
body {
  margin: 0;
  padding: 0;
  overflow: hidden;
  width: 100vw;
  height: 100vh;
  background: #BABED4;
}
canvas {
  display: block;
  border: 0;
}

/* At the top level of your code */
@media screen and (min-width: 900px) {
  canvas {
    border: 3px solid #4656D4;
  }
}