<div id="net">
  <a href="#" id="page1">page#1</a>
  <a href="#" id="page2">page#2</a>
  <a href="#" id="page3">page#3</a>
  <a href="#" id="page4">page#4</a>
</div>

#net a {
  position: absolute;
  left: -80px;
  transition: 0.3s;
  padding: 15px;
  width: 100px;
  text-decoration: none;
  font-size: 20px;
 
  border-radius: 0 5px 5px 0;
}

#net a:hover {
  left: 0;
}

#page1 {
  top: 20px;
  background-color: #960018;
 color: #fff;
}

#page2 {
  top: 80px;
  background-color: #007FFF;
 color: #fff;
}

#page3 {
  top: 140px;
  background-color: #66FF00;
color: #000;
}

#page4 {
  top: 200px;
  background-color: yellow;
color: #000;
}

<iframe src="https://www.netbax.net/tab/creation/hoverable-sidenav.html" style="width: 550px; height:550px;" frameborder="0"></iframe>