canvas {
  width: 100vw;
  height: 100vh;
  -webkit-box-shadow: inset 0px 0px 0px 1px #f00;
  -moz-box-shadow: inset 0px 0px 0px 1px #f00;
  box-shadow: inset 0px 0px 0px 1px #f00;
  display: block;
  object-fit: contain;
  position: absolute;
  left: 0;
  top: 0;
}