body {
  margin: 0;
  overflow: hidden;
  background-color: #000;
}

canvas {
  display: block;
}

.serve-btn {
    position: absolute;
    top: 20px;
    left: 20px;
    padding: 10px 20px;
    font-size: 16px;
    z-index: 1;
    cursor: pointer;
}