body {
  margin: 0;
  background-color: rgb(26, 26, 26);
  position: relative;
  height: 100vh;
}

#screen {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background: black;
  transition: background 0.5s ease-in;
}