html,
body {
  height: 100%;
  margin: 0;
}
main {
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}
canvas {
  max-height: 100%;
  max-width: 100%;
}
button{
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    overflow: auto;
    background: none;
    border: none;
    outline: none;
    appearance: none;
    z-index:  100;
}