Fit, scale and center image responsively to browser window (CSS)

Question

How do I have an image, irrespective of portrait or landscape:

• centered responsively both horizontally and vertically (remains centered as browser window is resized)
• occupies a fixed fraction of the browser window, scaling responsively
• preserves aspect ratio as browser window is resized

Answer 1

Here's a solution that satisfies all of the above with only basic CSS (no CSS3 required):

http://jsfiddle.net/dvidby0/sytj1uws/1/

HTML

<div class="container">
<!-- this is a landscape image-->
<img src="http://upload.wikimedia.org/wikipedia/commons/1/15/Cat_August_2010-4.jpg"/>
<!--or use this portrait image; still works
<img src="http://upload.wikimedia.org/wikipedia/commons/9/9d/Britishblue.jpg"/>
-->

CSS

.container {
width: 80%;
height: 80%;
position: absolute;    
margin:auto;
top:0;
bottom:0;
left:0;
right:0;
background-color: #aaa;
}

img {
max-width: 100%;
max-height: 100%;  
position: absolute;
margin:auto;
top:0;
bottom:0;
left:0;
right:0;
}