Run LESS in JSFiddle

HTML

<script src="http://lesscss.googlecode.com/files/less-1.3.0.min.js"></script>
<div class="parentDiv">
        <div>1</div>
        <div>2</div>
        <div>3</div>
        <div>4</div>
        <div>5</div>
</div>

CSS

.new_mixin (@n) {
    div {
        &:nth-of-type(n) {                
            position: absolute;
            top: @n * 20px;
            width: 50px;
            border: 1px solid #ff0;
        }
    }
}

.parentDiv {
    .new_mixin(1);
}

JavaScript

/*

    While we are waiting for JSFiddle to support LESS integration I figured
    I would get a work around sorted so I can still write it in here
    
    Twitter: @aaronlayton
*/

// Step 1: Select the style element and change it to text/less
$('head style[type="text/css"]').attr('type', 'text/less');

// Step 2: Tell LESS to refresh the styles
less.refreshStyles();

/* 
    You could put this as a oneliner and use it as a shim for JSFiddle

    (function(){ $('head style[type="text/css"]').attr('type', 'text/less');less.refreshStyles(); })()
    
*/