body:before{
  content:'>> SITIO DE PRUEBAS <<';
  position:absolute;
  color:#f53b3b;
  font-weight:bold;
  font-size:20px;
  animation: blink-animation 1s steps(5, start) infinite;
  -webkit-animation: blink-animation 1s steps(5, start) infinite;
}
@keyframes blink-animation {
  to {
    visibility: hidden;
  }
}
@-webkit-keyframes blink-animation {
  to {
    visibility: hidden;
  }
}