html {
  height: 100%;
  width: 100%;
}


button {
  width: 130px;
  height: 50px;
  position: absolute;
  top: calc(50% - 150px);
  left: calc(50% - 90px);
  background-color: white;
  z-index: 9999;
  line-height: 50px;
  text-align: center;
  color: black;
}