html {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
}
body {
  height: 100%;
  width: 100%;
  background: darkgrey;
}
div.logIn {
  height: 500px;
  width: 500px;
  background-color: grey;
  position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%);
}