A CodePen by Sara Soueidan. Responsive CSS3 Side Navigation Menu - Media Queries Transitions (resize the window slowly to see the transitions), nav items slide out on hover when it collapses on smaller screens.

index.html

<h1>Slowly resize screen to see the width transition</h1>
<div class="nav-container">
  <ul class="nav">
    <li class="active">
      <a href="#">
        <span class="icon-home"></span>
        <span class="text">home</span>
      </a>
    </li>
    <li>
      <a href="#">
        <span class="icon-user"></span>
        <span class="text">about</span>
      </a>
      </li>
    <li>
      <a href="#">
        <span class="icon-headphones"></span>
        <span class="text">Audio</span>
      </a>
      </li>
    <li>
      <a href="#">
        <span class="icon-picture"></span>
        <span class="text">Portfolio</span>    
      </a>
    </li>
    <li>
      <a href="#">
        <span class="icon-facetime-video"></span><span class="text">video</span>
      </a>
    </li>
  </ul>
</div>

script.js

$('li').click(function(){
  
  $(this).addClass('active')
       .siblings()
       .removeClass('active');
    
});

/*

Inspired by Asif Aleem's work: http://www.freebiesgallery.com/responsive-website-navigation/

Feel free to fork it and make it better, AND use it however u want, the whole functionality could, of course, have been done with jQuery alone, but I thought I'd try to do it with CSS3, to make use of media query transitions, and of course, just to practice more.
You can use this when changing orientation on a tablet or smart phone for example.. and of course, use ur creative minds for any more uses u can come up with :)

Follow me on Twitter: http://twitter.com/SaraSoueidan

*/

style.css

*{
  box-sizing: border-box;
}
body{
  height:100%;
  background-color: #444;
}
h1{
  font-size:1em;
  text-align:center;
  color: #eee;
  letter-spacing:1px;
  text-shadow: 1px 1px 1px rgba(0,0,0,0.5);
}
.nav-container{
  width:300px;
  margin-top:10px;
  box-shadow: 0 2px 2px 2px black;
  transition: all 0.3s linear;
}
.nav{
  list-style-type:none;
  margin:0;
  padding:0;
}
li{
  height:50px; 
  position:relative;
  background: linear-gradient(#292929, #242424);
}
a {
  border-top: 1px solid rgba(255,255,255,0.1);
  border-bottom: 1px solid black;
  text-decoration:none;
  display:block;
  height:100%;
  width:100%;
  line-height:50px;
  color:#bbb;
  text-transform: uppercase;
  font-weight: bold;
  padding-left:25%;
  border-left:5px solid transparent;
  letter-spacing:1px;
  transition: all 0.3s linear;
}
.active a{
  color: #B93632;
  border-left:5px solid #B93632;
  background-color: #1B1B1B;
  outline:0;
}
li:not(.active):hover a{
  color: #eee;
  border-left: 5px solid #FCFCFC;
  background-color: #1B1B1B;
}
span[class ^= "icon"]{
  position:absolute;
  left:20px;
  font-size: 1.5em;
  transition: all 0.3s linear;
}

@media only screen and (max-width : 860px){
  
  .text{
    display:none;
  }
  
  .nav-container , a{
    width: 70px;
    
  }
   
  a:hover{
    width:200px; 
    z-index:1;
    border-top: 1px solid rgba(255,255,255,0.1);
    border-bottom: 1px solid black;
    box-shadow: 0 0 1px 1px black;
  }
  
  a:hover  .text {
    display:block;
    padding-left:30%;
  }
}
@media only screen and (max-width : 480px){
  .nav-container, a{ width:50px;}
  span[class ^= "icon"]{ left:8px;}
}