body {
  margin: 0;
  background: lightblue;
  overflow: hidden;
}

canvas {
  display: block;
  margin: 0 auto;
  background: #ccc;
}

#jumpBtn {
  position: absolute;
  bottom: 20px;
  right: 20px;
  padding: 15px 20px;
  font-size: 24px;
  border-radius: 10px;
  background: #2196f3;
  color: white;
  border: none;
  display: none;
  z-index: 10;
}

@media (max-width: 768px) {
  #jumpBtn {
    display: block;
  }
}