Earlier this year, I wrote a post on proportional responsive css, detailing two techniques in order to create proportionally responsive elements. The third option I'll be detailing here is little more than an expansion on the padding solution, but one that will save you the need for an extra structural wrapper at the cost of out of the box browser compatibility.

The padding technique is based on the fact that top/bottom padding is relative to the width of its parent. Exploiting this behavior, you can easily create a rectangle that grows and shrinks proportionally. Once you have the proportional box, you can span (position:absolute and all sides set to 0) a deeper nested box across the parent box. For this technique you need two extra wrappers, though. One to set the padding (as it only works on the width of its parent), and one to span the content across the box.

/* html */

<section class="list"> 
  <div class="atom"> 
    <div class="content"> ... </div> 
  </div> 
  <div class="atom">...</div> 
</section> 

The .atom elements are our proportional blocks, the .content elements are the spanned elements that contain the actual content of the block. Now for the CSS:

 /* css */ 
.list {overflow:hidden;} 
.atom {width:25%; float:left; position:relative;} .
.atom:before {content:""; display:block; padding-top:100%;} 
.atom .content {position:absolute; left:0; right:0; top:0; bottom:0;} 

The trick is actually pretty simple. We simply use a pseudo-element to trigger the padding magic, which means we don't need the extra structural wrapper in the HTML. The pseudo-element is set to display:block, so it acts like a regular structural element, then it's given a padding depending on the ratio you want to support (100% makes a square).

The problem with pseudo-elements is that they are not supported in IE7. JavaScript fallbacks are easy to do (just insert a div with JS and apply the exact same styling), but ideal it is not. Then again, if you don't need to support IE7, this third technique makes things a lot easier.