doctype html
script src="https://code.jquery.com/jquery-3.1.1.slim.min.js"
.x 
.x
.x
css:
  .x {
    width:100px;height:100px;
    background-color:red;margin:5px;
    animation:blink 1s step-end 0s infinite alternate;
  }
  @keyframes blink{
    50% {opacity:0}
  }