body, html {
  margin: 0;
  padding: 0;
  height: 100%;
  background: #111;
  overflow: hidden;
}

#gameArea {
  position: relative;
  width: 100vw;
  height: 100vh;
  background: #222;
}

#ball {
  position: absolute;
  width: 50px;
  height: 50px;
  background: #0f0;
  border-radius: 50%;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}