Untitled

CSS Save image aspect ratio
<img src="big_image.png" style="max-width: 100px; max-height: 100px;" />

<div id='container'>
    <ul>
     <li>
    <img src="http://static.dezeen.com/uploads/2009/01/2-port-house-antwerp-by-zaha-hadid-architects-sqwu-2port-house_antwerp_02.jpg">
        </li>
          <li>
    <img src="http://static.dezeen.com/uploads/2009/01/2-port-house-antwerp-by-zaha-hadid-architects-sqwu-2port-house_antwerp_02.jpg">
        </li>
          <li>
    <img src="http://static.dezeen.com/uploads/2009/01/2-port-house-antwerp-by-zaha-hadid-architects-sqwu-2port-house_antwerp_02.jpg">
        </li>
    </ul>
</div>

#container{
    max-width:auto;
    max-height: auto;
    background: red;
}

img {
    max-width:20%;
    max-height: 20%;
}