body{
  background-image: url('https://upload.wikimedia.org/wikipedia/commons/c/cf/Casio_calculator_JS-20WK_in_201901_002.jpg');
  animation: myanim 3s infinite;
            background-position: bottom left;
            background-size: 50px;
}
h1 {
  color: darkgreen;
}
#result {
  background-color: white;
}
#container {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: lightgreen;
  border-radius: 1em;
  padding: 20px;
}