.modal-window {
  position: fixed;
  background-color: rgba(200, 200, 200, 0.75);
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 999;
  opacity: 0;
  pointer-events: none;
  -webkit-transition: all 0.3s;
  -moz-transition: all 0.3s;
  transition: all 0.3s;
}

.modal-window:target {
  opacity: 1;
  pointer-events: auto;
}

.modal-window>div {
  width: 400px;
  position: relative;
  margin: 10% auto;
  padding: 2rem;
  background: #fff;
  color: #444;
}

.modal-window header {
  font-weight: bold;
}

.modal-close {
  color: #aaa;
  line-height: 50px;
  font-size: 80%;
  position: absolute;
  right: 0;
  text-align: center;
  top: 0;
  width: 70px;
  text-decoration: none;
}

.modal-close:hover {
  color: #000;
}

.modal-window h1 {
  font-size: 150%;
  margin: 0 0 15px;
}

<!--<a href="#open-modal">Open Modal</a>-->
<!--<div id="open-modal" class="modal-window">-->
<!--    <div>-->
<!--        <a href="#modal-close" title="Close" class="modal-close">close &times;</a>-->
<!--        <h1>CSS Modal</h1>-->
<!--        <div>The quick brown fox jumped over the lazy dog.</div>-->
<!--    </div>-->
<!--</div>-->