Question: I'm looking for a way to do something like this:

```
// style.css
@def borderSize '2px';

.style {
  width: borderSize + 2;
  height: borderSize + 2;
}

```

where the width and height attributes would end up having values of 4px.

Answer: 
Mozilla kind-of-sort-of-not-really supports this with it's CSS `calc()` function.

This example shamelessly stolen (with attribution!) from [Ajaxian](http://ajaxian.com/archives/css-calc-in-the-house)

```
/*
* Two divs aligned, split up by a 1em margin
*/
#a {
  width:75%;
  margin-right: 1em;
}
#b {
  width: -moz-calc(25% - 1em);
}

```

It's not cross-browser, and it's probably only barely supported by even bleeding-edge versions of Firefox, but there's at least being progress made in that direction.
I would also love somehting like that, but it's not possible.
Even in CSS 3 their is nothing planned like this.

If you really want to make something like that, one possibility is to use
php and configure your webserver, so that .css files are parsed by php.

So you could do something like

```
<?
  $borderSize = 2;
?>

.style {
  width: <? borderSize+2 ?>px;
  height: <? borderSize+2 ?>px;
}

```

But as this is no 'standard' way, i think its better to not do it.