透明弹出窗口/按钮叠加（JQuery，CSS）

$("body").append(`<div class="popup">
  <ul>
    <li>Ex 1</li>
    <li>Ex 2</li>
    <li>Ex 3</li>
    <li>Ex 4</li>
  </ul>
</div>`)

body {
  margin:0;
  padding:0;
}

.popup {
  position:fixed;
  top:0;
  left:0;
  z-index:1;
  width:100%;
  height:100%;
  background:rgba(77,77,77,.4);
}

.popup > ul {
  list-style-type:none;
  padding:0;
  margin:0;
  position: absolute;
  top: 50%;
  width:100%;
  transform: translateY(-50%);
}

.popup > ul > li {
  background:green;
  display:inline-block;
  color:black;
  border:2px solid black;
  width:calc(25% - 8px);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>