CSS currently doesn't have a way to check for children (or, what would essentially be a 'parent selctor', something that often comes up as a wishful thought in discussions about css. Read more: http://css-tricks.com/parent-selectors-in-css/)
In order to style something like that, you'd have to use jQuery (or, javascript...)
$('ul').each(function () {
if ($(this).find('span').length) {
$(this).css({your style here});
}
}
If what you do is not dynamic, it would always be easiest to give a class to those lists beforehand and style them.