<div>BAD</div>

body,html{margin:0;height:100%;}
body{display:grid;place-content:center;}

div{
  padding:5vmin;
  color:white;
  background:#000;
  animation-delay:1s;
  animation-name:fadeIn;
  animation-duration:1s;
}

@keyframes fadeIn{
  from{
    opacity:0;
  }
  to{
    opacity:1;
    background:red;
  }
}