html,
body {
  width: 100%;
  height: 100%;
  padding: 0;
  margin: 0;
}

body {
    background-color: #282828;
    display: flex;
    justify-content: center;
    align-items: center;
}

canvas {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}


#download {
  display: none;
  position: absolute;
  bottom: 10px;
  right: 10px;
}

#download.visible {
    display: block;
}