html,
body {
  margin: 0;
  padding: 0;
  overflow: hidden;
  height: 100%;
}
.container {
  height: 100%;
  background-color: #333;
  background: url("../img/canvas.png");
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
}
canvas {
  position: absolute;
  left: 0;
}
.center {
  position: relative;
  width: 800px;
  height: 600px;
  box-shadow: 0 0 8px 8px black;
}