CSS: match a tag not containing another one

http://stackoverflow.com/questions/23427173/how-to-match-a-tag-not-containing-another-one?noredirect=1#comment35902829_23427173

HTML

<script src="http://cdnjs.cloudflare.com/ajax/libs/less.js/1.7.0/less.min.js"></script>
<ul>
    <li>Grain&nbsp;:
        <ul>
            <li>Baisse du rendement</li>
            <li>Sénescence plus rapide la plante</li>
            <li>Sensibilisation accrue à la fusariose des tiges</li>
        </ul>
    </li>
</ul>

CSS

ul { 
    &>li {
        &:after {
            content: " ;";
        }
        &:last-child:after {
            content: "(final end)";
        }

        &>ul { 
            li:last-child:after {
                content: " .";
            }
        }
    }
}

JavaScript

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